STATUS OF SEA TURTLES IN THE
ARAFURA AND TIMOR SEAS
A Literature Review
This report was prepared by Nicolas J. Pilcher, Marine Research
Foundation for The Arafura and Timor Seas Ecosystem Action Phase 2
(ATSEA-2) Project.
July 2021
Status of Sea Turtles in the Arafura
and Timor Seas
Copyright © 2021 Arafura and Timor Seas Ecosystem Action Phase 2 (ATSEA-2) Project
Authors:
Pilcher, Nicolas J.
Suggested Citation:
Pilcher, NJ, (2021). Status of Sea Turtles in the Arafura and Timor Seas. Report to the Arafura and Timor
Seas Ecosystem Action Phase 2 (ATSEA-2) Project, Bali, Indonesia. 83 p.
Disclaimer:
ATSEA-2 Project has published the information contained in this publication to assist public knowledge and
discussion, and to help improve the sustainable management of the Arafura and Timor Seas (ATS) region.
The contents of this publication do not necessarily reflect the views or policies of ATSEA-2 implementing
partners and its other participating organizations. The designation employed and the presentation do not
imply expression of opinion whatsoever on the part of ATSEA-2 concerning the legal status of any country
or territory, its authority or the delimitation of its boundaries.
Published by:
ATSEA-2 Regional Project Management Unit
Jl. Mertasari No. 140 Sidakarya,
Denpasar 80224, Bali, Indonesia
Telephone: +62 361 448 4147
Email: [email protected]
Website: https://atsea-program.com/
Cover Image: Loggerhead turtle hatchling © Nicolas Pilcher ∣ MRF
Printed in Denpasar, Bali, Indonesia
i | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
EXECUTIVE SUMMARY
Sea turtles are important species with multiple values to natural ecosystem processes, and to
customs and traditions of indigenous people of the Arafura and Timor Seas (ATS) Region. Sea
turtles have been utilised for food, trade and have been part of ceremonial practices for
thousands of years. Sea turtles also play important ecological roles, cropping seagrasses,
foraging on sponges on coral reefs, and acting as top and middle predators in marine
ecosystems. Sea turtles have also been subjected to pressures including bycatch in commercial
and artisanal fisheries, and in discarded fishing gears, climate change, egg and turtle take (legal
and illegal), light pollution, along with habitat loss and degradation.
The region is home to six species of sea turtle including green turtle (Chelonia mydas); hawksbill
(Eretmochelys imbricata); loggerhead (Caretta caretta); leatherback (Dermochelys coriacea); olive
ridley (Lepidochelys olivacea); and flatback turtle (Natator depressus). All species are listed as
Vulnerable, Endangered or Critically Endangered, and are subject of protection via a number of
National legislation instruments and via international conventions.
POPULATION DISTRIBUTION, CONNECTIVITY STATUS AND GENETIC STRUCTURE
Green turtles are distributed throughout the Arafura and Timor Seas, but generally remain in
coastal waters where they inhabit shallow water development and foraging areas. Nesting has
been documented throughout the northern shores of Australia and in the Torres Strait islands,
and also in the Aru Islands in Indonesia, where the majority of nesting occurs on Enu Island. There
is also green turtle nesting in Kaimana, in the northwest extend of Indonesia’s West Papua coast,
but little is known or quantified for the remainder of the Indonesian West Papua coast. Green
turtle nesting has been also reported for East Nusa Tenggara; and on the Tanimbar and Kei
Islands in the Moluccas. Green turtles disperse extensively within the ATS region and there is also
emigration into and immigration from other areas, such as northward into the Sulu and Sulawesi
Seas and Pacific Ocean, or westward into Indian Ocean. Green sea turtles in the Arafura and
Timor seas belong to two Regional Management Units, but 17 genetically distinct breeding stocks
have been identified among green turtles nesting throughout the Australasian region, four of
which occur within the ATS. Green turtle aggregations at feeding grounds are often derived from
multiple breeding stocks, and turtles can move great distances between foraging areas and
nesting sites. There are few studies of long-term trends for rookeries in the ATS region, and there
remains the need for implementation and ongoing monitoring at key green turtle rookeries to
confirm the abundance and trends in numbers of nesters at each key rookery.
Hawksbills nest on multiple islands scattered across the ATS region, but few estimates of
abundance are available. In Indonesia hawksbill nesting has been reported for Roti, Dana and
Semau Islands in East Nusa Tenggara; and also at the Tanimbar Islands and the Aru Islands in the
Moluccas. There is also nesting of hawksbills along the Kaimana coast and offshore islands in
West Papua. In Papua New Guinea there are several sites where nesting occurs, but the scattered
nature of the surveys and the survey durations do not permit an updated assessment of nesting
at a national level. In Timor-Leste, hawksbill nesting occurs on Jaco Island and on the beaches at
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | ii
Com, Tutuala and Lore in the east of the country. At least some of the post-nesting hawksbills
migrate from Timor-Leste to the northwest coast of Australia.
In Australia, hawksbills nest around much of the Northern Territory coastline and on virtually all
islands that have sandy beaches. The region may be home to over 5,000 nesters each year.
Hawksbill turtles from northeast Australia have been recorded in Vanuatu, Solomon Islands,
Papua New Guinea and elsewhere in the Great Barrier Reef. Hawksbill foraging aggregations are
typically mixed stocks of individuals originating from multiple nesting areas, but there is also a
trend of foraging turtles coming from nearby nesting beaches – that is, little dispersal from
hatchling to adult. There are two recognised genetic stocks of hawksbill turtle breeding in
Australia, and each of these stocks supports an annual nesting population of several thousand
females. Data on hawksbill nesting trends are not available within the ATS region given the lack
of long-term studies on these smaller rookeries. Hawksbill turtles are difficult to monitor for a
number of reasons: (a) small numbers of hawksbills nest on a wide variety of beaches across a
broad geographic area; (b) hawksbill beaches tend to be remote, inaccessible and sometimes so
narrow that the turtle leaves no crawl trace; and (c) hawksbill turtles exhibit large year-to-year
fluctuations in nesting numbers so that single year counts cannot be used to determine trends.
Loggerheads are widespread throughout ATS waters but there is no breeding by loggerhead
turtles in northern Australia, Indonesia, Papua New Guinea or Timor-Leste. Substantial movement
has been documented of post-nesting loggerhead turtles into foraging areas in the Arafura and
Timor Seas, with turtles following coastal routes along the Western and Northern Australia coast
and assumed foraging that lay predominantly in waters of North Australia. Loggerheads of the
southeast Indian Ocean are treated as a single Regional Management Unit (RMU), and this
includes nesting turtles from Western Australia and foraging turtles throughout the ATS region.
Little trend data exists to point to overall population trends.
Leatherback sea turtles migrate through ATS waters, and a handful of nesters use beaches in
Northern Australia. The leatherback turtle does not nest elsewhere in the ATS region.
Leatherbacks from Papua New Guinea or Indonesia generally do not move into the ATS region,
but a small proportion of leatherbacks do move down into the Arafura Sea. The west Pacific
leatherback turtle is considered a single RMU, and nesting in Australia has been in a continuous
decline, similar to that in Papua New Guinea.
Olive ridley turtles are moderately abundant in the ATS region, and nest on beaches in Australia,
Indonesia and Timor-Leste. However, nesting is dispersed and of low volume, and sometimes
confounded with hawksbill turtle nesting. There are records of olive ridley turtles from West
Papua moving into the Arafura Sea, and others that show how Australian olive ridley turtles may
remain in Australian waters. The genetic structure and population connectivity is highly
structured, and Australian and east Indonesian olive ridleys share many of the same haplotypes,
but also displayed substantial differences. There are no long-term studies on the olive ridley in
the ATS region and no indication of population trends.
The flatback turtle is unique in that is nests only in Australia, with some northward distribution of
foraging grounds. Foraging flatbacks have been encountered in neighbouring Papua New Guinea
and Indonesia but no nesting records for this species exist in those countries. Due to their nonoceanic nature, whereby flatback turtles are restricted to Australian waters and those of
iii | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
southern Papua New Guinea and Indonesia, the migration and habitat connectivity data for this
species is limited mostly to the Australian continental shelf and the Timor Sea. Genetic structure
of flatback turtles comprises seven genetic stocks, with geographic boundaries of rookeries
varying from 160km to 1,300km. Population sizes appear to be stable at present.
THREATS
Key threats include bycatch in commercial and artisanal fisheries, entanglement in and ingestion
of discarded fishing gears, predation, traditional turtle take, poaching and illegal egg harvests,
climate change and light pollution. Given the lack of a complete understanding of the magnitude
of impacts on sea turtle populations, it is not possible to accurately identify the highest and
lowest priority threats. For instance, while climate change may impact sea turtle populations, it is
currently unknown to what extent this occurs.
LEGAL INFRASTRUCTURE
Several provisions exist that provide protection measures to sea turtles including National legal
instruments, international conventions, fisheries management plans – including enforcement
measures, and indigenous community management plans. Each of these has certain limitations, but
there are also a number of strengths, such as the mandatory use of Turtle Excluder Devices in
Australia, and the collective community management in the Fly River region in Papua New Guinea.
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | iv
RINGKASAN EKSEKUTIF
Penyu adalah spesies bernilai penting bagi berbagai proses ekosistem alami, serta adat dan
tradisi masyarakat adat di Wilayah Laut Arafura dan Laut Timor (ATS). Penyu dimanfaatkan untuk
makanan, perdagangan dan sebagai bagian dari praktik upacara selama ribuan tahun. Tak hanya
itu, penyu juga memainkan peranan ekologis yang penting, diantaranya mengkonsumsi lamun,
mencari spons sebagai sumber pakan di terumbu karang, dan berperan sebagai predator puncak
dan menengah pada ekosistem laut. Meski demikian, penyu terus mengalami ancaman termasuk
sebagai tangkapan sampingan (bycatch) dalam perikanan komersial dan artisanal, dan terhadap
alat tangkap yang dibuang, perubahan iklim, pengambilan telur dan penyu (legal dan ilegal),
polusi cahaya, serta degradasi dan hilangnya habitat.
Wilayah ATS merupakan rumah bagi enam spesies penyu termasuk penyu hijau Chelonia mydas;
sisik Eretmochelys imbricata; tempayan Caretta caretta; belimbing Dermochelys coriacea; lekang
Lepidochelys olivacea; dan pipih Natator depressus. Semua terdaftar sebagai spesies Rentan,
Terancam Punah atau Sangat Terancam Punah, dan berada dalam perlindungan sejumlah
instrumen perundang-undangan Nasional dan melalui konvensi internasional.
DISTRIBUSI POPULASI, STATUS KONEKTIVITAS DAN STRUKTUR GENETIK
Penyu hijau tersebar di seluruh Wilayah ATS, tetapi umumnya berada di perairan pesisir yang
merupakan wilayah berkembang dan mencari pakan. Lokasi peneluran penyu telah
didokumentasikan di seluruh pantai utara Australia dan di kepulauan Selat Torres, dan juga di
Kepulauan Aru di Indonesia, khususnya di Pulau Enu. Penyu hijau juga ditemukan bertelur di
Kaimana, di sepanjang barat laut pantai Papua Barat Indonesia, tetapi hanya sedikit informasi
terkait penyu di pantai Papua Barat Indonesia lainnya. Habitat peneluran penyu hijau juga
dilaporkan di Nusa Tenggara Timur; Kepulauan Tanimbar, dan Kepulauan Kei di Maluku. Penyu
hijau tersebar secara luas di dalam wilayah ATS, serta penyu hijau tersebut juga melakukan
imigrasi dari dan emigrasi ke daerah lain, seperti ke utara menuju Laut Sulu dan Sulawesi dan
Samudera Pasifik atau ke barat menuju Samudera Hindia . Penyu hijau di laut Arafura dan laut
Timor termasuk dalam satu Unit Pengelolaan Regional, namun teridentifikasi 17 stok
penangkaran penyu hijau yang berbeda secara genetik yang bertelur di wilayah Australasia, yang
4 berada di wilayah ATS. Penyu hijau yang beragregasi di tempat mencari pakan sering kali
berasal dari beberapa stok penangkaran, dan penyu dapat berpindah dengan jarak yang sangat
jauh antara area mencari pakan dan lokasi peneluran. Selanjutnya, terdapat beberapa studi
tentang tren jangka panjang untuk habitat peneluran di wilayah ATSEA, serta masih
membutuhkan implementasi dan pemantauan berkelanjutan di habitat peneluran utama penyu
hijau untuk mengkonfirmasi kelimpahan dan tren jumlah sarang di setiap penangkaran utama.
Lokasi peneluran penyu sisik tersebar di beberapa pulau di wilayah ATSEA, tetapi estimasi
kelimpahan yang tersedia masih terbatas. Lokasi peneluran penyu sisik dilaporkan di Pulau
Rote, Ndana dan Semau di Nusa Tenggara Timur; dan juga di Kepulauan Tanimbar dan
Kepulauan Aru di Maluku. Penyu sisik juga ditemukan bertelur di sepanjang pantai Kaimana dan
pulau-pulau lepas pantai di Papua Barat. Papua Nugini juga memiliki beberapa lokasi bertelur,
v | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
tetapi kondisi yang tersebar dan durasi yang tidak menentu menyebabkan sulit untuk
melakukan penilaian terkini terkait lokasi peneluran pada tingkat nasional. Di Timor-Leste,
penyu sisik bertelur di Pulau Jaco, beberapa pantai di Com, pantai Tutuala, dan Lore di bagian
Timur. Beberapa penyu sisik yang telah bertelur di Timor-Leste bermigrasi ke pesisir barat laut
Australia, Lokasi peneluran penyu sisik di Australia ditemukan di sebagian besar garis pantai
wilayah federal Australia bagian utara, Northern Territory (NT) dan di hampir seluruh pulau
dengan pantai berpasir. Wilayah ini diprediksi menjadi rumah bagi lebih dari 5.000 penyu
petelur setiap tahun. Penyu sisik dari timur laut Australia ditemukan di Vanuatu, Kepulauan
Solomon, Papua Nugini dan tempat lain di Great Barrier Reef. Agregasi penyu sisik di tempat
mencari pakan biasanya terdiri atas campuran individu yang berasal dari beberapa lokasi
peneluran. Namun, ditemukan juga kecenderungan penyu yang berasal dari lokasi pantai
peneluran terdekat untuk mencari pakan – dikenal sebagai penyebaran yang sempit dari tukik
hingga dewasa. Penyu sisik yang bertelur di Australia teridentifikasi memiliki dua stok genetik,
dan masing-masing stok ini mendukung populasi peneluran tahunan beberapa ribu betina. Data
tentang tren peneluran penyu sisik tidak tersedia di wilayah ATSEA karena kurangnya studi
jangka panjang tentang habitat peneluran yang lebih kecil ini. Pemantauan penyu sisik sulit
dilakukan karena beberapa alasan: (a) jumlah sarang penyu sisik yang kecil di berbagai pantai
peneluran di wilayah geografis yang luas; (b) pantai penyu sisik cenderung terpencil, tidak
dapat diakses dan terkadang sangat sempit sehingga penyu tidak meninggalkan jejak; dan (c)
penyu sisik menunjukkan fluktuasi jumlah sarang yang besar dari tahun ke tahun sehingga
hitungan satu tahun tidak dapat digunakan untuk menentukan tren peneluran.
Penyu tempayan tersebar luas di seluruh perairan ATSEA tetapi tidak ada habitat peneluran
penyu tempayan di Australia utara, Indonesia, Papua Nugini atau Timor-Leste. Pergerakan
substansial penyu tempayan telah didokumentasikan dari pascabertelur menuju ke daerah
mencari pakan di Laut Arafura dan Laut Timor, mengikuti rute pesisir di sepanjang pesisir
Australia Barat dan Utara, dan diasumsikan lokasi mencari pakan yang sebagian besar terletak di
perairan Australia Utara. Penyu tempayan di tenggara Samudra Hindia diperlakukan sebagai unit
pengelolaan regional (UPR – Regional Management Unit/RMU) tunggal, termasuk penyu yang
bertelur di Australia Barat dan penyu yang mencari pakan di seluruh wilayah ATSEA. Adapun, data
tren yang menunjukkan kecenderungan populasi secara keseluruhan masih sangat terbatas.
Penyu belimbing bermigrasi melalui perairan ATSEA, dan sejumlah kecil penyu yang bersarang di
pantai Australia Utara. Tidak ditemukan habitat peneluran penyu belimbing lainnya di kawasan
ATSEA. Penyu belimbing dari Papua Nugini atau Indonesia umumnya tidak melalui kawasan
ATSEA, tetapi sebagian kecil penyu belimbing bergerak turun ke Laut Arafura. Penyu belimbing
Pasifik barat dianggap sebagai UPR tunggal, dan peneluran di Australia terus mengalami
penurunan, hal serupa juga terjadi di Papua Nugini.
Penyu lekang cukup melimpah di wilayah ATSEA, dan mereka memanfaatkan pantai-pantai di
Australia, Indonesia dan Timor-Leste untuk bertelur. Namun, sarang mereka bersifat tersebar dan
dengan volume yang rendah, sehingga kerap terkecoh dengan sarang penyu sisik. Penyu lekang
tercatat bergerak dari Papua Barat ke Laut Arafura dan informasi lainnya menunjukkan
bagaimana penyu lekang Australia menetap di perairan Australia. Struktur genetik dan
konektivitas populasi penyu lekang sangat terstruktur, dan memiliki banyak kesamaan haplotype
antara penyu lekang Australia dan Indonesia timur, namun disaat yang bersamaan juga
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | vi
menunjukkan perbedaan yang substansial. Tidak tersedia studi jangka panjang tentang penyu
lekang dan indikasi tren populasi di wilayah ATSEA.
Penyu pipih memiliki keunikan karena hanya bersarang di Australia, dengan tempat mencari
pakan yang tersebar ke arah utara. Akan tetapi, penyu pipih tercatat mencari pakan di negara
tetangga Papua Nugini dan Indonesia, namun tidak ditemukan habitat peneluran di kedua negara
tersebut. Karena sifatnya yang non-oceanic, di mana penyu pipih terbatas di perairan Australia,
Papua Nugini bagian selatan dan Indonesia, data migrasi dan konektivitas habitat untuk spesies
ini sebagian besar terbatas pada landas kontinen Australia dan Laut Timor. Struktur genetik
penyu pipih terdiri dari tujuh stok genetik, dengan batas geografis habitat peneluran bervariasi
dari 160 km hingga 1.300 km. Untuk saat ini, jumlah populasi terlihat stabil.
ANCAMAN
Ancaman utama penyu antara lain, tangkapan sampingan (bycatch) dalam perikanan komersial
dan artisanal, terjerat dan menelan alat tangkap yang dibuang, predasi, pengambilan penyu oleh
masyarakat untuk keperluan tradisi, perburuan dan pengambilan telur illegal, perubahan iklim
dan polusi cahaya. Mengingat kurangnya pemahaman yang lengkap tentang besarnya dampak
kegiatan manusia terhadap populasi penyu, tidak memungkinkan untuk secara akurat
mengidentifikasi ancaman prioritas tertinggi dan terendah. Misalnya, saat ini tidak diketahui
sejauh mana perubahan iklim dapat berdampak pada populasi penyu.
INFRASTRUKTUR HUKUM
Adapun, beberapa ketentuan hukum telah memberikan perlindungan terhadap penyu termasuk
diantaranya instrumen hukum nasional, konvensi internasional, rencana pengelolaan perikanan –
termasuk upaya penegakan, dan rencana pengelolaan masyarakat adat. Masing-masing
ketentuan tersebut memiliki keterbatasan, tetapi juga memiliki sejumlah kelebihan, seperti
mewajibkan penggunaan Turtle Excluder Devices di Australia, dan pengelolaan komunitas kolektif
di wilayah Fly River di Papua Nugini.
vii | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
ACKNOWLEDGEMENTS
This work was jointly funded by the Global Environment Facility (GEF), Partnerships in
Environmental Management for the Seas of East Asia (PEMSEA), and United Nations
Development Program (UNDP) under the auspices of the Arafura and Timor Seas Ecosystem
Action Phase II (ATSEA-2) project. The Regional Project Management Unit (RPMU) of ATSEA-2
gratefully acknowledges the work of the author and the inputs from national and regional
consultation participants conducted in March 2021. The RPMU extends gratitude to the ATSEA-2
Regional Steering Committee (RSC) for its guidance and approval in December 2021.
The RPMU recognises the enthusiastic participation and generous contributions provided by the
sea turtle experts from the 4 Arafura and Timor Seas (ATS) countries- Col Limpus, Duane March,
Kathryn McKenna, Mick Guinea, Moni Carlisle (Australia), Adrianus Sembiring, Deasy Natalia
Lontoh, Dian Dewi, Dwi Suprapti, I Made Jaya Ratha, Ida Ayu Dian Kusuma Dewi, Jan Manuputty,
Matheus Halim, Mochammad Riyanto, Prabowo, Retno Kusuma Ningrum, Windia Adnyana,
Yusup Jentewo (Indonesia), Marzena Ann Marinjembi, Phelameya J. Haiveta, Ralph Mana, Rita
Goiye, Vagi Rei (Papua New Guinea), Anselmo Amaral and Celestino da Cunha Baretto (TimorLeste) during the Sea Turtle Expert Workshop (STEW) held in April 2022 as recommended by the
2021 4
th RSC meeting. Finally, we extend our gratitude to Dr. Kiki Dethmers who led the STEW,
compiled the inputs and further finalised the document.
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | viii
CONTENTS
Executive Summary................................................................................................................................i
Ringkasan Eksekutif.............................................................................................................................iv
Contents .............................................................................................................................................. viii
Table of Figures..................................................................................................................................x
Tables................................................................................................................................................ xii
Acknowledgements ............................................................................................................................vii
Chapter 1. Introduction and Background..............................................................................................1
Chapter 2. IUCN Status .......................................................................................................................... 3
Chapter 3. Regional Management Units..............................................................................................4
Chapter 4. Management Units ............................................................................................................. 5
Chapter 5. Green Sea Turtles ................................................................................................................6
5.1 Distribution & Migrations.............................................................................................................6
5.2 Genetic Structure ........................................................................................................................11
5.3 Population Trends .......................................................................................................................13
Chapter 6. Hawksbill Sea Turtles........................................................................................................ 14
6.1 Distribution & Migrations........................................................................................................... 14
6.2 Genetic Structure....................................................................................................................... 18
6.3 Population Trends......................................................................................................................20
Chapter 7. Loggerhead Sea Turtles .................................................................................................... 22
7.1 Distribution & Migrations........................................................................................................... 22
7.2 Genetic Structure ....................................................................................................................... 24
7.3 Population Trends ...................................................................................................................... 24
Chapter 8. Leatherback Sea Turtles ...................................................................................................26
8.1 Distribution & Migrations...........................................................................................................26
8.2 Genetic Structure.......................................................................................................................28
8.3 Population Trends......................................................................................................................28
Chapter 9. Olive Ridley Sea Turtles ....................................................................................................29
9.1 Distribution & Migrations...........................................................................................................29
9.2 Genetic Structure....................................................................................................................... 33
9.3 Population Trends......................................................................................................................34
Chapter 10. Flatback Sea Turtles ........................................................................................................ 35
10.1 Distribution & Migrations ......................................................................................................... 35
10.2 Genetic Structure......................................................................................................................40
10.3 Population Trends .................................................................................................................... 41
Chapter 11. Threats ..............................................................................................................................43
ix | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
11.1 Bycatch in fisheries ....................................................................................................................43
11.2 Ghost nets..................................................................................................................................47
11.3 Predation ...................................................................................................................................48
11.4 Traditional Turtle Take..............................................................................................................49
11.5 Illegal Turtle take........................................................................................................................51
11.6 Egg collection............................................................................................................................ 52
11.7 Climate impacts (storms, temperature, erosion).................................................................... 53
11.8 Light Pollution........................................................................................................................... 55
Chapter 12. Legal Infrastructure......................................................................................................... 57
12.1 National Legal Provisions.......................................................................................................... 57
12.2 Relevant International Conventions ........................................................................................ 57
12.3 Fisheries Management ............................................................................................................. 57
12.4 Indigenous Community Management.....................................................................................58
References ...........................................................................................................................................60
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | x
Table of Figures
Figure 1. Map of the Arafura and Timor Seas region.............................................................................1
Figure 2. Green turtle distribution in the ATS region. Darker colours indicate greater number of
records per 1o cells. Data includes nesting locations and at-sea data from satellite tracking.
Image source: OBIS-Seamap 2021 ................................................................................................6
Figure 3. Green turtle movements in the Gulf of Carpentaria (adapted from Kennet et al. 2004)...8
Figure 4. Top: Satellite tracks of turtles from the Norwest Shelf in Western Australia (red), the
NWS-Kimberly stock (green) and the Scott-Browse stock (purple). Bottom: Movements
colour-coded by activity. Image source: Ferreira et al. 2020 .....................................................9
Figure 5. Top: Foraging distributions of green turtles using an occupancy index off Kimberly &
Scott Reef (g); Coburg Peninsula & Tiwi Islands (h); and Gulf of Carpentaria (i). Plates j, k & l
as above using percentage of foraging turtles. Image source: Ferreira et al. 2020 ............... 10
Figure 6a. Post-nesting migrations of green turtles from Merir and Helen Islands, Palau. Image
source: Klain et al. 2007 ...............................................................................................................11
Figure 6b. Post-nesting migrations of a green turtle from Jaco island - Nino Konis Santana NP,
Timor-Leste to Cobourg Peninsula – Ggarik Gunak Barlu NP, Australia. Image source: CI
Timor-Leste...................................................................................................................................11
Figure 7. Location of 17 genetically distinct breeding stocks or management units as inferred from
analysis of geographical structure of mtDNA variants and position of the genetic barrier
(dashed line), indicating the major genetic discontinuity between the turtles west of Cape
York and those of the Pacific Ocean. Image source: Dethmers et al. 2006..............................12
Figure 8. Trends in number of green turtle nests deposited each year on key Western Australian
beaches. Image source: IUCN MTSG, unpublished ....................................................................13
Figure 9. Hawksbill movements from the northern GBR into the Arafura Sea. Image source: Miller
et al. 1998..................................................................................................................................... 16
Figure 10. Migration routes of hawksbill turtles tagged in the Arnavon Islands, Solomon Islands.
Image source: Hamilton et al. 2015............................................................................................ 16
Figure 11. Migration routes of hawksbill turtles tagged in Australia and neighbouring countries.
Image source: Limpus 2007b......................................................................................................17
Figure 12. Migration routes of hawksbill turtles tagged in Timor-Leste. Image source:
Conservation International, unpublished data; https://zoatrack.org/projects/560/analysis ...17
Figure 13. Hawksbill movements within the Gulf of Carpentaria. Image source: Hoenner et al. 2015
...................................................................................................................................................... 18
Figure 14. Modelled distribution and clustering probability of post-hatchling turtles from (a)
North East Island and (b) Milman Island, whose locations are shown by crosses. Red
markers indicate spatial clustering of high probabilities, whereas light blue markers indicate
spatial clustering of low probabilities. Image source: Hoenner et al. 2015............................. 19
Figure 15. Frequencies of control region haplotypes (739 bp) from each of nine mtDNA lineages in
the hawksbill turtle rookeries. Image source: Arantes et al. 2020 ........................................... 19
Figure 16. Annual hawksbill nesting at three Indonesia rookeries. Data source: Dermawan 2002.20
Figure 17. Projected trend in numbers of hawksbills nesting on Milman Island, Australia. Data
source: Bell et al. 2020 .................................................................................................................21
Figure 18. Loggerhead turtle distribution in the ATS region. Darker colours indicate greater
number of records per 1o cells. Image source: OBIS-Seamap 2021.......................................... 22
xi | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
Figure 19. Global satellite telemetry data for loggerhead turtles. Image source: SWOT Report No.
XV ................................................................................................................................................. 23
Figure 20. Movements of loggerhead turtles from Western Australia. Image source: Tucker et al.
2020.............................................................................................................................................. 23
Figure 21. Foraging grounds of turtles tracked from Western Australia. Image source: Waayers et
al. 2015.......................................................................................................................................... 24
Figure 22. Trend in nesting loggerheads at Northwest Cape, WA. Image source: Prince 2000 ...... 25
Figure 23. Leatherback turtle distribution in the ATS region. Darker colours indicate greater
number of records per 1o cells. Image source: OBIS-Seamap 2021..........................................26
Figure 24. Regional leatherback turtle movements showing migrations of West Papua turtles into
the Arafura Sea. Image source: Benson et al. 2011.................................................................... 27
Figure 25. Decline of leatherback nesting at Jamirsba Medi. Leatherback nesting abundance
(number of nests) trend at Jamursba Medi from 1984–2011 and Wermon from 2002–2011.
Image source: Tapilatu et al. 2013 ..............................................................................................28
Figure 26. Olive ridley turtle distribution in the ATS region. Darker colours indicate greater
number of records per 1o cells. Image source: OBIS-Seamap 2021..........................................29
Figure 27. Migration routes of an olive ridley turtle tagged in Timor-Leste. Image source:
Conservation International, unpublished data; https://zoatrack.org/projects/560/analysis ..30
Figure 28. Olive ridley turtle movements from West Papua into the Arafura Sea. Image source:
Doi et al. 2019................................................................................................................................31
Figure 29a. Movement patterns during post-nesting migration and foraging of 4 olive ridley
turtles tracked from the Wessell Islands in the Northern Territory of Australia. Image source:
McMahon et al. 2007....................................................................................................................31
Figure 29b. Post-release movements of eight Olive ridley turtles from on Turtle Melville Island,
northern Australia, in 2004 and 2005. Image source: Whiting et al. 2007b............................. 32
Figure 29c. Post-release movements of eight Olive ridley turtles from on Turtle Melville Island,
northern c. High-density areas for olive ridleys in the ATS based on post-release movements
of 27 olive ridley turtles (Dethmers et al. 2016)......................................................................... 32
Figure 30. Haplotype distribution across the Indonesian olive ridley population. Pie charts
represent the proportion of haplotypes defined in the network at each site. Image source:
Madduppa et al. 2021 .................................................................................................................. 33
Figure 31. Flatback turtle distribution in the ATS region. Darker colours indicate greater number of
records per 1o cells. Image source: OBIS-Seamap 2021 ............................................................ 35
Figure 32. Flatback turtle distribution in the northern Australian region. Image source: Australia
Species Profile and Threats Database, Accessed May 26, 2021................................................36
Figure 33. Flatback turtle dispersal from the Lacapede Islands in Western Australia. Image source:
Adapted from Thums et al. 2017................................................................................................. 37
Figure 34. Migration routes and foraging areas for five female flatback turtles after nesting at Warul
Kawa in 2013 (left) and six female flatback turtles after nesting at Warul Kawa in 2014. Image
source: Hamann et al. 2015 ..........................................................................................................38
Figure 35. State-space model position estimates of flatback sea turtles from Western Australia.
Tracks are coloured by behavioural mode: yellow: inter-nesting; blue: outward transit; red:
foraging; green: other transit. Image source: Thumbs et al. 2018 ...........................................38
Figure 36. Post-nesting dispersal of flatback turtles showing the seven foraging area hotspots
across NW Australia shown at a 2 km pixel scale. Image source: Poutinen & Thums 2016 ....39
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | xii
Figure 37. Dispersal of post-nesting flatback turtles from Cape Domett, NT: S. Whiting et al.,
unpublished.................................................................................................................................39
Figure 38. Distribution of the nine most common mitochondrial DNA haplotypes, and combined
‘other’ category, sampled from 17 flatback turtle (Natator depressus) rookeries. Image
source: FitzSimmons et al. 2020.................................................................................................40
Figure 39. Designated flatback turtle (Natator depressus) genetic stocks based on the analyses of
17 rookeries across their range. Image source: FitzSimmons et al. 2020................................. 41
Figure 40. Nesting abundance of flatback turtles (Natator depressus) at Kakadu National Park,
NT. Image source: Groom et al. 2017.......................................................................................... 41
Figure 41. Nesting abundance of flatback turtles (Natator depressus) at Bare Sand Island, NT.
Image source: M Guinea, 2020 ...................................................................................................42
Figure 42. Spatial distribution of cumulative turtle interactions with Commonwealth-managed
fisheries, 2000–2013. A: Groote Eyland; B: Sir Edward Pellew Islands; C: Wellesley Islands.
Image source: Riskas et al. 2016 .................................................................................................44
Figure 43. Spatial distribution patterns of cumulative turtle interactions with Northern Territorymanaged fisheries, 2000–2013. E: Tiwi Islands; F: East Arnhem Land. Image source: Riskas et
al. 2016 .........................................................................................................................................44
Tables
Table 1. Estimates of turtle bycatch at a selection of locations in Indonesia ...................................46
Table 2. Proportion of turtle bycatch by fishing gears in Indonesia .................................................46
1 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
CHAPTER 1. INTRODUCTION AND BACKGROUND
Sea turtles are important species with multiple values to natural ecosystem processes, and to
customs and traditions of indigenous peoples of the Arafura and Timor Seas (ATS) Region; Figure
1). Sea turtles have been utilised for food, trade and have been part of ceremonial practices for
thousands of years. Sea turtles also play important ecological roles, cropping seagrasses,
foraging on sponges on coral reefs, and acting as top and middle predators in marine
ecosystems. However, sea turtles have been subjected to increasing pressure as threats such as
bycatch in commercial and artisanal fisheries have increased, and climate change threatens
important nesting and feeding areas and sea turtle reproductive biology. The ATS Region is home
to six species of sea turtles:
• The green turtle (Chelonia mydas)
• The hawksbill turtle (Eretmochelys imbricata)
• The loggerhead turtle (Caretta caretta)
• The leatherback turtle (Dermochelys coriacea)
• The olive ridley turtle (Lepidochelys olivacea); and
• The flatback turtle (Natator depressus)
Figure 1. Map of the Arafura and Timor Seas region
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 2
A clear understanding of population status is necessary for the development of targeted and
prioritised management and conservation action. This status review will serve as the basis for the
development of a focussed management strategy for the four countries that border the Arafura
and Timor Seas (Australia, Indonesia, Papua New Guinea and Timor-Leste). Cognisant of the
existence of National management and/ or recovery plans, management initiatives embedded in
international agreements, and traditional indigenous management plans, the outcomes of this
present initiative are to focus on the immediate timeframe (3-5 years) and pressing conservation
intervention needs that will safeguard sea turtle populations in the ATS region.
3 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
CHAPTER 2. IUCN STATUS
Among the most recognised assessments population status are the status assessments
conducted for the IUCN Red List. This assessment process objectively evaluates the trend in
numbers of a species, the available habitat, limitations to habitat use, whether the population is
fragmented, whether the population is genetically distinct, and a suite of other factors to
produce a risk of extinction assessment that is comparable across species. That is, the risk of
extinction to an orchid uses the same assessment process as that for a marine turtle, and the
resulting risk extinction assessments are directly comparable. For sea turtles the most common
criterion on which to determine risk extinction assessments is the trend in numbers of nesting
turtles over time. This is because counts of nesting females and clutches of eggs on beaches is
the most common type of data collected for sea turtles. These assessments are undertaken by
members of the IUCN Species Survival Commission (SSC) Marine Turtle Specialist Group (MTSG).
The 2020 IUCN Red List of Threatened Species lists the six marine turtle species found in the ATS
region as follows:
• Leatherback (Dermochelys coriacea): Vulnerable (global)
Critically endangered (West Pacific subpopulation)
• Hawksbill (Eretmochelys imbricata): Critically endangered (global)
• Loggerhead Caretta caretta): Vulnerable (global)
Near threatened (Southeast Indian Ocean
subpopulation)
• Green (Chelonia mydas): Endangered (global)
• Olive Ridley (Lepidochelys olivacea): Vulnerable (global)
• Flatback (Natator depressus): Data deficient (this does not mean that there is no
data available, but merely that the data have not
yet been compiled and assessed using IUCN
criteria). However, under Australia’s Environment
Protection and Biodiversity Conservation Act
1999), where flatbacks are endemic, they are listed
as vulnerable.
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 4
CHAPTER 3. REGIONAL MANAGEMENT UNITS
The MTSG recognised long ago that it was unrealistic to assess sea turtles at a global scale due to
the vast differences in trends at different locations, and in recent years has conducted
assessments at a level commensurate with their movements and genetic linkages. This more
regionally-restricted assessment of extinction risk is conducted at a level of Regional
Management Units, or RMUs (Wallace et al. 2010). The RMU framework is a solution to the
challenge of how to organize marine turtles into units of protection above the level of nesting
populations, but below the level of species, within regional entities that might be on independent
evolutionary trajectories. As new assessments are conducted by the MTSG, they now address sea
turtle extinction risk at the RMU level. The Leatherback subpopulation assessment listed in
Section 2.0 is an example of a recent assessments conducted using the RMU framework. The
current recognised Regional Management Units of sea turtles in the ATS region are as follows:
Green (2) : Southwest Pacific, Southeast Indian Ocean
Hawksbill (3) : Southeast Indian Ocean, West Pacific / Southeast Asia, Southwest Pacific
Loggerhead (1) : Southeast Indian Ocean
Leatherback (1) : West Pacific
Flatback (2) : Southeast Indian Ocean, Southwest Pacific
Olive Ridley (1) : West Pacific
5 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
CHAPTER 4. MANAGEMENT UNITS
A more regionally restricted method of grouping turtle populations based primarily on genetic
stocks is described by Management Units, or MUs (while the RMUs described above also address
movements and connectivity and dispersal to foraging habitats). Green turtle Management Units
were described by Dethmers et al. (2006); hawksbill Management Units were described by
Broderick et al. (1994) and Vargas et al. (2016); and Management Units for olive ridley turtles
were described by Jensen et al. (2013). More recently, Management Units for flatback turtles
were described by FitzSimmons et al. (2020). Leatherback genetics structure by Dutton et al.
(1999) that defined only one stock for the western Pacific and Southeast Asia. Australia does not
further break the western Pacific stock down into Management Units. Loggerhead genetic
structure was described by Bowen et al. (1994, 1995) and there are two distinct breeding stocks
in the west Pacific region. Australia considers the western Australian stock ranging up into the
Northern Territory to be a single Management Unit. This extensive genetic analysis work based
out of Australia considered the linkages between Australian nesting and foraging turtle species
with those of neighbouring countries, and the Management Units for turtles in the Arafura and
Timor Seas, where these are described, are worthy of recognition, as follows:
Green : (1) Gulf of Carpentaria, (2) Ashmore Reef, (3) Scott Reef / Browse Island, (4) Aru
Islands.
Hawksbill : (1) Great Barrier Reef (GBR), Torres Strait and Arnhem Land; (2) northwest shelf of
Western Australia.
Loggerhead: One single Management Unit.
Leatherback: One single Management Unit.
Olive Ridley: (1) Cape York, (2) Northern Territory.
Flatback : (1) Joseph Bonaparte Gulf, (2) Arafura Sea.
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 6
CHAPTER 5. GREEN SEA TURTLES
5.1 DISTRIBUTION & MIGRATIONS
Green turtles are distributed throughout the Arafura and Timor Seas, but generally remain in
coastal waters where, presumably, they inhabit shallow water development and foraging areas
(Figure 2). Nesting has been documented in Australia and in the Torres Strait islands (Limpus
2007a), and also in the Aru Islands in Indonesia (Enu, Jeh and Karang Islands; Dethmers 2010),
where the majority of nesting occurs on Enu Island. There is also green turtle nesting in Kaimana,
in the northwest extend of Indonesia’s West Papua coast (Tapilatu et al. 2017), but little is known
or quantified for the remainder of the Indonesian West Papua coast. Green turtle nesting has
been also reported for Roti and Dana Islands (East Nusa Tengggara); and on the Tanimbar Islands
in the Moluccas, and on the Kei Islands (Schulz 1989). Schulz suggested estimates of annual
nesting by green turtles as follows: 3,600 to 5,400 in the Aru and Tanimbar Island groups in the
Moluccas; and 40-50 at the Kei islands. Dethmers (2010) estimates appear to support these
estimates, at least for the Aru Islands. There are no ongoing monitoring programmes at other
sites to provide estimates of annual nester abundance.
Figure 2. Green turtle distribution in the ATS region. Darker colours indicate greater number of records per 1o
cells. Data includes nesting locations and at-sea data from satellite tracking. Image source: OBIS-Seamap 2021
In the Torres Strait, straddling Australia and Papua New Guinea, the majority of green turtle
nesting occurs on the eastern islands and these turtles are more likely to be associated with the
northern Great Barrier Reef (nGBR) region. Green turtle nesting in the Torres Strait occurs on
Bramble Anchor, Don Dower, Maclennan and Underdown Cays. There are no reports of green
turtle nesting on the Papua New Guinea mainland fronting the ATS region. In Timor-Leste, Jaco
7 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
Island and the beaches of Com, Tutuala and Lore have been identified as turtle nesting sites
(Nunes 2001, Amaral pers. comm.), with green turtles nesting between February and August.
Other breeding sites may exist on the south coast of Timor-Leste. Green turtles are also
reported to nest in low numbers in Tibar bay, west of Dili, and at Ulmera (Eisemberg et al.
2014). Nest protection programs meare run by local communities in the east of the country and
coordinated by CI. Since 2018, these programmes are providing the first species specific nesting
data for Timor- Leste.
In Australia, nesting sites are extensive and occur along much of the northern region. In the
eastern Gulf of Carpentaria nesting occurs at the Wellesly Group (Bountiful, Pisonia & Rock
Islands). An order of magnitude estimate of the annual nesting population in the Wellesley Group
is ~5,000 females (Limpus 2007a). In the western Gulf of Carpentaria nesting occurs along the
Arnhem Land coast, Groote Eyland and Sir Edward Pellew Islands (SEP; Limpus 2007a and
references therein). A preliminary estimate of the size of the annual green turtle nesting
population for eastern Arnhem Land is thousands of females annually (at present there are no
precise population size estimates, nor an understanding of population size trends). The principal
nesting sites include: mainland beaches from Binanangoi Point (Port Bradshaw) south to Cape
Shield, especially between Binanangoi Point and Wanyanmera Point; northern beaches of
Woodah Island; eastern Groote Eylandt area, especially North East Island and south-eastern
Groote Eylandt (south from Ilyungmadja Pt.; south from Ungwanba Point; Marangala Bay); and
Sandy Islet. In the SEP the majority of sea turtle nesting activity occurred on two islands, West
Island and Vanderlin Island. The low-density green turtle on the mainland and adjacent islands of
northeast Arnhem Land that lie south from Cape Arnhem are within the Dhimurru Indigenous
Protected Area. Low-density green turtle nesting also occurs on the Crocodile Islands, including
Murrungga island and Gurriba island, northern Arnhemland. Gurriba was declared turtle
sanctuary by the traditional owners of the land. The land and sea country are managed by the
Crocodile Island rangers, based in Milingimbi. Declaration of Indigenous Protected Areas over
Lhanapuy and Groote Eylandt means that the majority of the green turtle nesting habitat in
western Gulf of Carpentaria is now on indigenous protected and managed lands.
Hamann et al. (2006) suggested the green turtle nesting population of the Sir Edward Pellew
Islands was in the order of 100s of females per year. However, they indicate that this came from a
single season survey and that there may be substantial changes from year to year.
Western Australia supports one of the largest green turtle populations in the world and may
potentially be the largest in the Indian Ocean (Limpus 2007a). The principal rookeries include the
Lacepede Islands, Monte Bello Islands, Barrow Island, North West Cape and Browse Island.
Numerous small rookeries also occur in Western Australia. While most of these sites lie outside of
the ATS region, there is significant migration of post-nesting turtles into the Timor and Arafura
seas and large expanses of foraging areas (Ferreira et al. 2020). Limpus (2007a) indicated that in
an average nesting season, tens of thousands of green turtles may breed on western Australian
beaches. Recent data from key rookeries in Western Australia (IUCN MTSG, unpublished)
suggests this number may be lower but still significant, ca. 5,000 annual nesters.
Post-breeding migration of turtles in the Gulf of Carpentaria has been derived from flipper tag
recoveries from the Wellesley Group Rookeries and from satellite telemetry of females from
eastern Arnhem Land Rookeries (Figure 3; Kennett et al. 2004). All foraging areas linked to this
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 8
breeding assemblage by tag recovery and satellite tracking lie within the Gulf of Carpentaria, and
this appears to be a very regionally-restricted foraging distribution (Limpus 2007a).
Figure 3. Green turtle movements in the Gulf of Carpentaria (adapted from Kennet et al. 2004)
Post-nesting migrations of 96 green turtles from Western Australia highlight the linkages of this
turtle stock to the Arafura and Timor Seas, and indicate that turtles remain in coastal waters for
most of the time and spend most of their time in Australian waters (Figure 4; Ferreira et al. 2020).
However, the study also documented turtles moving to Sumba Island (Indonesia) and West
Papua (Indonesia) and Torres Strait, passing through Papua New Guinea waters (Ferreira et al
2020). Key foraging areas for western Australian green turtles lie predominantly close to the
Australian mainland (Figure 5; Ferreira et al 2020).
There is also green turtle nesting on the Australian islands in the Timor Sea. The National Nature
Reserve (NNR) in the Indian Ocean encompasses three vegetated cays which support marine
turtle nesting (West Island, Middle Islet, and East Islet) and one unvegetated cay (Cartier Reef)
that also is a green turtle rookery (Whiting et al. 2000). Most nesting occurs on West Island
9 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
(Whiting et al. 2000). Early season nesting counts suggest that the total green turtle nesting
population is of the order of hundreds of females annually (Guinea 1995, Whiting et al. 2000).
There is also a small green turtle population nesting on Scott Reef.
Figure 4. Top: Satellite tracks of turtles from the Norwest Shelf in Western Australia (red), the NWSKimberly stock (green) and the Scott-Browse stock (purple). Bottom: Movements colour-coded by activity.
Image source: Ferreira et al. 2020
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 10
Limpus (2007a) documented migrations of nGBR and southern Great Barrier Reef (sGBR) turtles
into Gulf of Carpentaria foraging grounds from flipper tag recoveries, and two satellite-tracked
green turtles from Palau moved south into Indonesian waters (Figure 6a; Klain et al. 2007),
indicating there is substantial immigration / emigration of green turtles in the ATS region to other
areas. Post-nesting migrations of a green turtle from Jaco island - Nino Konis Santana NP, Timor
LesteTimor-Leste to Cobourg Peninsula – Ggarik Gunak Barlu NP, Australia was also recorded
(Figure 6b).
Figure 5. Top: Foraging distributions of green turtles using an occupancy index off Kimberly & Scott Reef (g);
Coburg Peninsula & Tiwi Islands (h); and Gulf of Carpentaria (i). Plates j, k & l as above using percentage of
foraging turtles. Image source: Ferreira et al. 2020
11 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
Figure 6a. Post-nesting migrations of green turtles from Merir and Helen Islands, Palau. Image source: Klain et
al. 2007
Figure 7b. Post-nesting migrations of a green turtle from Jaco island - Nino Konis Santana NP, Timor-Leste to
Cobourg Peninsula – Ggarik Gunak Barlu NP, Australia. Image source: CI Timor-Leste
5.2 GENETIC STRUCTURE
Green sea turtles in the Arafura and Timor seas belong to a single RMU. However, Moritz et al.
(2002) described smaller management units, or Ecologically Significant Units, that might be more
applicable to understanding finer-scale differences in population structure. Subsequently,
Dethmers et al. (2006) indicated there were 17 genetically distinct breeding stocks for turtles
foraging in Australasian waters, and that these individual rookeries or groups of rookeries were
generally separated by more than 500 km. Of note, this study demonstrated a significant
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 12
discontinuity in genetic structure between Pacific Ocean stocks and those found further to the
west (Figure 7). That is, the turtles in the Arafura and Timor Seas are genetically distinct from those
green turtles that breed and forage in the Pacific. Dethmers et al. (2010) assessed linkages between
nesting and foraging grounds via migration data and found that green turtle aggregations at each
of the feeding grounds were derived from multiple breeding stocks. The geographic distance
between breeding and feeding habitat strongly influenced whether a breeding population
contributed to a feeding ground; however, neither distance nor size of a breeding population was a
good predictor of the extent of their contribution (Dethmers et al. 2010).
Figure 8. Location of 17 genetically distinct breeding stocks or management units as inferred from analysis of
geographical structure of mtDNA variants and position of the genetic barrier (dashed line), indicating the
major genetic discontinuity between the turtles west of Cape York and those of the Pacific Ocean. Image
source: Dethmers et al. 2006
Mixed-stock estimates at four of the feeding grounds (Ashmore Reef, Field Islands, Aru islands
and Sir Edward Pellew Islands) revealed a dominance of a single stock, with a mean contribution
of 50% or more. This means that the Gulf of Carpentaria comprised one genetic stock, or
Management Unit. For Ashmore Reef and Sir Edward Pellew Islands, this involved the
geographically most proximate breeding stock at Aru and the Gulf of Carpentaria, respectively,
both within a distance of 200 km. However, at the Ashmore Reef feeding ground, 75.4% of the
contributions were assigned to the North-west Shelf stock, 960 km distant. Interestingly, the
Ashmore Reef stock (at ~50km distance) had little representation at Ashmore Reef while, in
contrast, 11.2% of turtles at the Cobourg Peninsula feeding grounds were estimated to have
originated from the Ashmore Reef stock, 950km away. This study is a clear example of how some
turtles move great distances between foraging areas and nesting sites, while there may be more
suitable areas closer to home, and worthy of consideration in approaches to management and
conservation of sea turtles in the Arafura and Timor Seas.
13 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
5.3 POPULATION TRENDS
There are few studies of long-term trends for rookeries in the ATS region. This is related to a lack
of ongoing monitoring programmes at those key beaches in the ATS region – which more often
than not are sampled opportunistically or as part of specific studies. As part of a recent IUCN Red
List Assessment, numbers of green turtles at key Western Australian rookeries were used to
indicate population trends (Figure 8), and these trends might reflect green turtle nesting trends
elsewhere along the northern rookeries in Australia. However, there remains the need for
implementation and ongoing monitoring at key green turtle rookeries in the Gulf of Carpentaria
and along the beaches of the Northern Territory to confirm the abundance and trends in
numbers of nesters at each key rookery.
Figure 9. Trends in number of green turtle nests deposited each year on key Western Australian beaches.
Image source: IUCN MTSG, unpublished
0
2,000
4,000
6,000
8,000
10,000
12,000
14,000
16,000
1987 1992 1997 2002 2007 2012
Number of clutches
Barrow Is Ningaloo NW Cape Cape Range NP
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 14
CHAPTER 6. HAWKSBILL SEA TURTLES
6.1 DISTRIBUTION & MIGRATIONS
Hawksbills nest on multiple islands scattered across the ATS region, but few estimates of
abundance are available. In Indonesia hawksbill nesting has been reported for Roti, Dana and
Semau Islands in East Nusa Tenggara; and also at the Tanimbar Islands and the Aru Islands in the
Moluccas (Tomascik et al. 1997). However, they provide no estimates of rookery size. Tapilatu et
al. (2017) indicate there is nesting of hawksbills along the Kaimana coast and offshore islands,
although this site lies north of the ATS region, but similarly do not provide estimates of rookery
size. Hawksbills were also reported for the Aru islands by Dethmers (2010), again with no rookery
size estimates (although her study was aimed primarily at green turtles). While Asaad et al. (2018)
indicate hawksbills were widespread throughout the Coral Triangle region, they did not indicate
large assemblages or hawksbills in the Arafura and Timor seas. Similarly, Mortimer & Donnelly
(2008) do not indicate any major nesting sites for hawksbills in the Indonesian ATS region. It is
likely then that the hawksbill nesting sites in the Indonesian reaches of the ATS region are
common, widespread, but of small size.
In Papua New Guinea, Kinch (2020) reports on several sites where nesting occurs, but the
scattered nature of the surveys and the survey durations do not permit an updated assessment
of nesting at a national level. It is suggested that the total annual nesters in PNG may be <500
turtles per year, but it is unknown how many of these are from the Torres Straits islands.
In Timor-Leste, hawksbill turtles nest on Jaco Island and Com, Tutuala and Lore beaches,
between January and July. While there are no publications describing hawksbill nesting in TimorLeste in the published literature, hawksbills nesting in the Nino Konis Santana National Park have
been tracked with satellite transmitters moving through the Timor Sea and south to Western
Australia (Figure 12). Nest protection programmes are run by local communities in the east of the
country and coordinated by CI. Since 2018, these programmes are providing the first species
specific nesting data for Timor- Leste.
In Australia, Hamann et al. (2006) indicate hawksbill nesting in the Sir Edward Pellew islands in
the range of <100 turtles per year. There were also 220 nesting females in 2009 and 580 females
in 2010 at the Groote Eylandt archipelago in the western Gulf of Carpentaria (Hoenner et al.
2016). Hawksbill turtles nest around much of the Northern Territory coastline and on virtually all
islands that have sandy beaches (Chatto 1998). In general, most of this nesting occurs east of
Darwin with the best areas found between Bathurst and North Goulburn Islands, from the east of
Elcho Island, east and south to the southern end of Groote Eylandt, and the outer Sir Edward
Pellew Islands. The size of the nesting population at each of the numerous hawksbill rookeries in
the Gulf of Carpentaria remains incompletely surveyed (Limpus et al. 2000). Approximately 40
nesting sites were recorded for hawksbill in northeastern Arnhem Land during a spring aerial
survey (Limpus et al. 2000). Additional low density nesting beaches probably occur in the region;
however, their identification may be obscured by concurrent olive ridley nesting for those sites
where positive distinction between these species could not be made for all tracks observed.
15 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
Limpus et al. (2000) found 12 sites with an estimated > 100 nesting female hawksbill annually as
follows:
1. Outer islands of the English Company Islands area: Truant Island and Bromby Island.
2. Northeastern Groote Eylandt area: North East Island, Hawk Island, and Lane Island, which
are the extreme northeastern beaches of Groote Eylandt. This area appeared to be the most
significant area for hawksbill nesting in the Northern Territory.
3. Northwestern Groote Eylandt area: Hawknest Island, Bustard Island, and the small island
southwest of Bustard Island.
4. Southeastern Groote Eylandt area: Two small islands of Cape Beatrice and the southeast
coast of Groote Eylandt.
Some low-density nesting also occurs within the Gurig National Park on the Coburg Peninsula. For
each site with high-density nesting there was a series of lower density nesting sites in the vicinity
(Limpus 2007b). Most of the hawksbill rookeries of Arnhem Land lie outside National Park or
other habitat managed for conservation purposes except for the low-density hawksbill on the
mainland and adjacent islands of northeast Arnhem, and the land south from Cape Arnhem that
are within the Dhimurru Indigenous Protected Area.
There have been no detailed monitoring studies of the size of the annual hawksbill breeding
population at any of the Arnhem Land hawksbill rookeries (Limpus 2007b), and Limpus et al.
(2000) suggested a preliminary estimate of the current size of the annual hawksbill nesting
population for eastern Arnhem Land of ~2,500 females annually.
In Western Australia the Dampier Archipelago supports the largest hawksbill rookery in Australia
(~1,000 females nesting annually; Limpus 2007b), but there are no long-term quantified census
statistics to determine population trends or current abundance. Sporadic to low-density nesting
occurs over a much wider area, including the Ashmore Reef National Nature Refuge (Guinea
1995). Outside of the ATS region, but with migratory links to the ATS region, hawksbill turtles
nest in low density on multiple islands throughout the nGBR and Torres Strait areas (Limpus
1980, Limpus & Miller (2008), with Milman Island historically being one of the largest rookeries.
However, current estimates suggest the annual number of nesters at Milman Island is down to
~200, and Bell et al. (2020) predict the species could be extirpated by 2036.
There is limited data on hawksbill movements within the ATS Region and neighbouring countries.
Hawksbill turtles from northeast Australia have been recorded in Vanuatu, Solomon Islands,
Papua New Guinea and elsewhere in the Great Barrier Reef (Figure 6-1; Miller et al. 1998). One
flipper tag recovery from a hawksbill on Milman Island was recovered in Merauke (Figure 9;
Miller et al. 1998), but numerous turtles tracked from the Solomon Islands (the closest large
rookery outside of the ATS region) did not enter the Gulf of Carpentaria (Figure 10; Hamilton et
al. 2015). It appears the movements in and out of the Torres Strait may be limited only to
hawksbills from Australian rookeries and foraging areas. This is supported by flipper tag recovery
data presented by Limpus (Figure 11; 2007b). While some hawksbills from Timor-Leste move
south into the Timor Sea and Western Australia (Figure 12), there is likely substantial movement
of this species northwest and northeast into other Indonesian sites.
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 16
Figure 10. Hawksbill movements from the northern GBR into the Arafura Sea. Image source: Miller et al. 1998
Figure 11. Migration routes of hawksbill turtles tagged in the Arnavon Islands, Solomon Islands. Image source:
Hamilton et al. 2015
17 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
Figure 12. Migration routes of hawksbill turtles tagged in Australia and neighbouring countries. Image source:
Limpus 2007b
Figure 13. Migration routes of hawksbill turtles tagged in Timor-Leste. Image source: Conservation
International, unpublished data; https://zoatrack.org/projects/560/analysis
Limited flipper tagging data also has demonstrated that northeast Australia nesting hawksbills
have been found in Papua New Guinea, and nesting PNG hawksbills have been reported within
their Australian foraging range. Hoenner et al. (2015) reported that post-nesting female turtles
tagged within the Gulf of Carpentaria remained in the Gulf, suggesting minimal dispersal of adult
females from these rookeries (Figure 13). This same study also noted that key rookeries likely
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 18
seed areas in close proximity, and that post-hatchling turtles from these sites might seed areas
in the Torres Straits and the northern Coral Sea (Figure 14). This study modelled the dispersal of
hatchlings from two key rookeries in Australia and demonstrated how those from North East
Island in the Western Gulf of Carpentaria were more likely to remain in the ATS region
(Hoenner et al. 2015).
Figure 14. Hawksbill movements within the Gulf of Carpentaria. Image source: Hoenner et al. 2015
6.2 GENETIC STRUCTURE
A study on the global phylogeography of hawksbill turtles was recently undertaken by Arantes
et al. (2020). They noted that hawksbill foraging aggregations are typically mixed stocks of
individuals originating from multiple nesting areas, but there was also a trend of foraging
turtles coming from nearby nesting beaches – that is, little dispersal from hatchling to adult.
This study identified that Western Australia, Solomon Islands and Eastern Pacific hawksbills
were related – and interestingly this group was also related to the Persian Gulf, while the east
Pacific hawksbills formed another group, and a third group occurred in the Northern Territory
and North Queensland, Australia (Figure 15). Vargas et al. (2016) noted that hawksbill turtles
had a complex pattern of phylogeography, showing a weak isolation by distance and evidence
of multiple colonization events. This explains the shared haplotypes across much of the Pacific
region (pink colours, Figure 15).
19 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
Figure 15. Modelled distribution and clustering probability of post-hatchling turtles from (a) North East Island
and (b) Milman Island, whose locations are shown by crosses. Red markers indicate spatial clustering of high
probabilities, whereas light blue markers indicate spatial clustering of low probabilities. Image source:
Hoenner et al. 2015
Figure 16. Frequencies of control region haplotypes (739 bp) from each of nine mtDNA lineages in the hawksbill
turtle rookeries. Image source: Arantes et al. 2020
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 20
Findings by Arantes et al. (2020) were mirrored by findings using mtDNA studies within Australia
(Broderick et al. 1994). There are two recognised genetic stocks of hawksbill turtle breeding in
Australia (Moritz et al. 2002, Dutton et al. 2002), and each of these stocks supports an annual
nesting population of several thousand females (Limpus & Miller 2008). Genetic analysis
indicated that there was one stock that incorporated the hawksbill rookeries of the northern
Great Barrier Reef (nGBR), Torres Strait and Arnhem Land that was independent of a second
stock that breeds at rookeries on the northwest shelf of Western Australia (Broderick et al.
1994). Limpus (2007b) indicates that the GBR and Torres Strait turtles are unlikely to be
interbreeding with Arnhem Land turtles given differences in breeding timing.
6.3 POPULATION TRENDS
Data on hawksbill nesting trends are not available for the rookeries within the ATS region given
the lack of long-term studies on these smaller rookeries. Hawksbill turtles are difficult to monitor
for a number of reasons: (a) small numbers of hawksbills nest on a wide variety of beaches across
a broad geographic area; (b) hawksbill beaches tend to be remote, inaccessible and sometimes
so narrow that the turtle leaves no crawl trace; and (c) hawksbill turtles exhibit large year-to-year
fluctuations in nesting numbers so that single year counts cannot be used to determine trends.
Outside of the ATS region, data are available for three different locations in Indonesia (Alas
Purwo National Park, East Java; Jamursba-Medi beach, West Papua; and Sukamade beach, Meru
Betiri, East Java (Figure 16; Dermawan 2002), and for one site in Australia.
At the Indonesian sites there has been a general decline in nesting, predominantly due to the
harvesting of hawksbill turtles for their shell (Dermawan 2002). In Australia, Milman Island was
considered one of the most important hawksbill rookeries (Miller et al. 1995), but has witnessed
severe declines in the last three decades (Figure 17; Bell et al. 2020).
Figure 17. Annual hawksbill nesting at three Indonesia rookeries. Data source: Dermawan 2002
21 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
Figure 18. Projected trend in numbers of hawksbills nesting on Milman Island, Australia. Data source: Bell et al.
2020
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 22
CHAPTER 7. LOGGERHEAD SEA TURTLES
7.1 DISTRIBUTION & MIGRATIONS
Loggerheads are widespread throughout ATS waters (Figure 18, and Figure 19) but there is no
breeding by loggerhead turtles in northern Australia, Indonesia, Papua New Guinea or TimorLeste. The nearest nesting to the ATS region occurs in central Western Australia, from Shark Bay
to the southern Northwest Shelf (Limpus & Limpus 2003). Nesting loggerheads have been
flipper-tagged on Dirk Hartog Island nearly every year since 1993-1994 as part of a mark-recapture
program started by the Western Australian Marine Turtle Project (Prince 2000, Reinhold &
Whiting 2014). Dirk Hartog Island hosts approximately 70% of all loggerhead turtle nesting in WA,
with an estimated 1,000 – 3,000 females nesting at this site annually (Baldwin et al. 2003 Limpus,
2007c). It was believed the annual nesting population for the entire stock was of the order of
several thousand females (Baldwin et al. 2003), however, during 1998, 1999, 2000 and 2008, over
1,400 turtles were tagged at Dirk Hartog during several two-week peak periods (WAMTP
unpublished data, Reinhold & Whiting 2014), indicating annual nesting numbers are likely
substantially greater than previously estimated.
Substantial movement has been documented of post-nesting loggerhead turtles into foraging
areas in the Arafura and Timor Seas (e.g. Figure 20; Tucker et al. 2020). These turtles followed
coastal routes along the Western and Northern Australia coast, and assumed foraging that lay
predominantly in waters of North Australia (Figure 21)
Figure 19. Loggerhead turtle distribution in the ATS region. Darker colours indicate greater number of records
per 1o cells. Image source: OBIS-Seamap 2021
23 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
Figure 20. Global satellite telemetry data for loggerhead turtles. Image source: SWOT Report No. XV
Figure 21. Movements of loggerhead turtles from Western Australia. Image source: Tucker et al. 2020
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 24
Figure 22. Foraging grounds of turtles tracked from Western Australia. Image source: Waayers et al. 2015
7.2 GENETIC STRUCTURE
Loggerheads of the southeast Indian Ocean are treated as a single RMU (Wallace et al. 2010), and
this includes nesting turtles from Western Australia and foraging turtles throughout the ATS
region. The nesting populations of the various loggerhead rookeries in Western Australia, from
Shark Bay to the southern Northwest Shelf, are treated as a single interbreeding stock and
independent of the other stocks that breed in eastern Australia and elsewhere in the east Indian
Ocean (Bowen et al. 1994; Dutton et al. 2002, FitzSimmons et. al. 1996).
7.3 POPULATION TRENDS
While the western Australia nesting population is reported to number about 1,000 to 2,000
turtles annually (Baldwin et al. 2003), long-term census data from any index beach from which
population trends can be assessed come from only a few sites. At the Northwest Cape (Figure 22;
Prince 2000) the trend appears to show a fluctuating but steady trend, at least until 2000. In
contrast, Thomson et al. (2016) documented a steady decline from ~840 to ~450 nets at Gnarloo
on the mainland coast, and the trend at a State level likely warrants investigation.
25 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
Figure 23. Trend in nesting loggerheads at Northwest Cape, WA. Image source: Prince 2000
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 26
CHAPTER 8. LEATHERBACK SEA TURTLES
8.1 DISTRIBUTION & MIGRATIONS
Leatherback sea turtles migrate through ATS waters (Figure 23), and a handful of nesters use
beaches in Northern Australia. Scattered nesting may also occur on the beaches along the south
coast of Timor-Leste. The leatherback turtle does not nest elsewhere in the ATS region, but the
nearest rookery is on Buru Island, located just to the north in the Ceram Sea. The largest western
Pacific rookery lies further north in West Papua, Indonesia.
In Australia, low-density nesting has been recorded at Wreck Rock Beaches and Rules Beach,
southern Queensland and at the Coburg Peninsula and Arnhem Land, Northern Territory.
Sporadic nesting by 0–3 females per year were also recorded on the southern Queensland coast
between northern Hervey Bay (Bundaberg) and Roundhill Head (28 nesting attempts recorded
from 1968 to 1990) in the late 1970s and early 1980s (Limpus & McLachlan, 1994; Limpus et al.
1984). Nesting appears to have declined since that time (Limpus 2007d). Based on these figures
and trends it is estimated <3 turtles nest each year in Australia.
Although outside the ATS region, but with important migratory links (Figure 24), the key nesting
beaches in Indonesia are at Jamursba Medi and at Warmon, West Papua province.
Figure 24. Leatherback turtle distribution in the ATS region. Darker colours indicate greater number of records
per 1o cells. Image source: OBIS-Seamap 2021
27 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
Figure 25. Regional leatherback turtle movements showing migrations of West Papua turtles into the Arafura
Sea. Image source: Benson et al. 2011
Hitipeuw et al. (2007) recorded 1,865 and 3,601 nests at Jamursba Medi in 2003 and 2004,
respectively; and 1,788 and 2,881 nests are Warmon in 2003 and 2004. Hitipeuw et al. (2007)
surmised the number of annual nesters at Jamursba Medi was 501 to 660 in 2003; and 667 to 879
in 2004 after adjusting for season length. This number has continued to decline, and the number
of females nesting annually as of 2011 was estimated to be <400 during the boreal summer and
131 during the austral summer, based on estimated clutch frequency and clutch interval (Tapilatu
et al. 2013). However, most recently in 2021, 2,500 nests were recorded in Jamursba Medi and
Wermon (Lontoh pers. comm.). In 2017 WWF-Indonesia started annual surveys of the 12.4 km
beach of Fenaleisela, Buru Island and recorded an average of 250 leatherback nests per year
(Suprapti pers. comm.).
Leatherbacks from Papua New Guinea or Indonesia generally do not move into the ATS region,
but a small proportion of leatherbacks do move down into the Arafura Sea (Benson et al. 2011).
While turtles nest year round on Buru island, there are distinct peaks in the cold-season (NW
monsoon, November/December) and in the hot-season (end of the SE monsoon (June/July). The
cold-season nesters migrate to the south, towards the Lesser Sunda islands and into the Timor
Sea / Indian Ocean, while the hot-season nesters move northwards towards the Sulu-Sulawesi
region (Suprapti pers.com).
There are several accounts of leatherback turtles caught as by-catch by Timorese fishing boats
operating off the Timorese coast. There are also several reports of leatherback turtles coming
ashore on the south coast of Timor-Leste (Amaral pers. comm.).
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 28
8.2 GENETIC STRUCTURE
The west Pacific leatherback turtle is considered a single RMU (Wallace et al. 2010). In the west
Pacific, genetic analysis by using mitochondrial deoxyribonucleic acid sequences identified a total
of six haplotypes among the 106 samples analysed for Solomon Islands, Papua, and Papua New
Guinea, including a unique common haplotype that is only found in the western Pacific
populations (Dutton et al. 2007). The genetic signature of the Buru Island leatherback turtles has
yet to be determined.
8.3 POPULATION TRENDS
No data is available on trends of nesters in Australia, but Limpus (2007d) reported these to be
declining. Outside of the ATS region, there has been a continuous decline in nesting of
leatherbacks in West Papua (Figure 25), attributed in large part to terrestrial predators (Hitipeuw
et al. 2007, Tapilatu et al. 2013).
Figure 26. Decline of leatherback nesting at Jamirsba Medi. Leatherback nesting abundance (number of nests)
trend at Jamursba Medi from 1984–2011 and Wermon from 2002–2011. Image source: Tapilatu et al. 2013
29 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
CHAPTER 9. OLIVE RIDLEY SEA TURTLES
9.1 DISTRIBUTION & MIGRATIONS
Olive ridley turtles are moderately abundant in the ATS region (Figure 26), and nest on beaches in
Australia, Indonesia and Timor-Leste. However, nesting is dispersed and of low volume, and
sometimes confounded with hawksbill turtle nesting.
In Australia, olive ridley nesting occurs from the western coastline of Cape York, in the east,
westward to Fog Bay, NT (Whiting 1997). Olive ridleys have been recorded nesting on both
mainland and on island beaches, but mainly on islands (Chatto & Baker 2008). Low-density
nesting occurs along the northwestern coast of Cape York Peninsula between Weipa and Bamaga
(Limpus & Roper, 1977; Limpus et al. 1983, Limpus 2007e). The balance of nesting occurs in the
Northern Territory with minor nesting in Western Australia (Limpus 2007e). Over most of their
range in the Northern Territory (which includes little of the western coast of the NT) they nest in
low numbers. However, on some beaches (e.g. along the northern coast of the Tiwi Islands and
some islands in north eastern Arnhem Land) they nest in nationally significant numbers in the
order of several hundred nesters (Whiting et al. 2007a, Chatto & Baker 2008). The majority of
nesting occurs in the Northern Territory, and it is likely that the total annual nester abundance in
the north and east reaches of Australia is ~500 turtles per year. Olive ridleys also forage in north
Australian waters (Prince et al. 2010; see also Figure 22) based on direct observations and
captures in fisheries.
Figure 27. Olive ridley turtle distribution in the ATS region. Darker colours indicate greater number of records
per 1o cells. Image source: OBIS-Seamap 2021
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 30
Spring (1982) recorded olive ridley nesting in Papua New Guinea. However, none is known for the
islands and coastline fronting the ATS region.
In Timor-Leste, olive ridleys nest on Jaco Island and the beaches of Com, Tutuala and Lore
(Amaral pers. comm.) between February and August. While there are no publications describing
olive ridley nesting in Timor-Leste in the published literature, an olive ridley turtle nesting in the
Nino Konis Santana National Park was tracked with a satellite transmitter moving through the
Timor Sea and south to Western Australia (Figure 27a). Nest protection programmes are run by
local communities in the east of the country and coordinated by CI. Since 2018, these
programmes are providing the first species specific nesting data for Timor-Leste.
Figure 28. Migration routes of an olive ridley turtle tagged in Timor-Leste. Image source: Conservation
International, unpublished data; https://zoatrack.org/projects/560/analysis
There are records of olive ridley turtles from West Papua moving into the Arafura Sea (Doi et al.
2019; Figure 28), and several studies that indicated Australian olive ridley turtles may remain in
Australian waters (e.g. McMahon et al. 2007; Figure 29a, Whiting et al. 2007b; Figure 29b). Postnesting olive ridleys from the Crocodile islands moved northward into the ATS (Dethmers et al.
2016). Analysis of combined tracking data of 27 olive ridleys released from various locations
throughout Indonesia and north Australia (including those from the studies mentioned above),
appear to indicate some high-density aggregation areas in the ATS (Figure 29c).
31 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
Figure 29. Olive ridley turtle movements from West Papua into the Arafura Sea. Image source: Doi et al. 2019
Figure 30a. Movement patterns during post-nesting migration and foraging of 4 olive ridley turtles tracked
from the Wessell Islands in the Northern Territory of Australia. Image source: McMahon et al. 2007
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 32
Figure 31b. Post-release movements of eight Olive ridley turtles from on Turtle Melville Island, northern
Australia, in 2004 and 2005. Image source: Whiting et al. 2007b
Figure 32c. Post-release movements of eight Olive ridley turtles from on Turtle Melville Island, northern c. Highdensity areas for olive ridleys in the ATS based on post-release movements of 27 olive ridley turtles (Dethmers
et al. 2016)
33 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
In Indonesia, olive ridley turtles were not recorded in the ATS by Tomascik et al. (1997), but
nesting has been documented in Tuafanu and in Kwatisore Cenderawasih Bay (based on samples
collected by Madduppa et al. 2021). Dethmers (2010) indicated olive ridleys did not nest in the Aru
islands. Olive ridley nesting is better known in Indonesia at sites outside of the ATS region (e.g.
Alas Purwo National Park) and within the ATS the olive ridley likely nests at a handful of small and
diffuse rookeries.
9.2 GENETIC STRUCTURE
Bowen et al. (1998) demonstrated strong geographic partitioning of mtDNA lineages between
the Indo-West Pacific region and the East Pacific. Few studies have looked at genetics of olive
ridleys in the west Pacific, primarily because of their diffuse nesting. A recent study was
conducted to determine the genetic structure and population connectivity of olive ridley turtles
across the Indonesian archipelago, that indicated the Indonesian olive ridley stocks were highly
structured (Figure 30). While Australian and east Indonesian olive ridleys shared many of the
same haplotypes, there appeared to be substantial differences between the two countries
(Madduppa et al. 2021).
This was supported by genetic analyses of olive ridleys entangled in ghost nets in Northern
Australia, which indicated the turtles came from nesting populations within the Northern
Territory, but also that haplotypes not found in the Northern Territory were recorded, suggesting
turtles may have come from Indonesia, Timor-Leste or Papua New Guinea (Jensen et al. 2013).
Figure 33. Haplotype distribution across the Indonesian olive ridley population. Pie charts represent the
proportion of haplotypes defined in the network at each site. Image source: Madduppa et al. 2021
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 34
9.3 POPULATION TRENDS
There are no long-term studies on the olive ridley in the ATS region and no indication of
population trends. Outside of the region, olive ridley numbers have increased in the Alas Purwo
National Park, attributed primarily to conservation efforts, including nest relocation (Kurniawan
& Gitayana 2020). There are no indications that olive ridley turtle numbers in the ATS region have
increased or decreased, but accidental capture in fisheries and entanglement in ghost nets
appears to be frequent and is cause for concern. In Australia, there was an estimated 90% loss of
nests to pig predation on western Cape York (Limpus 2009) that is currently being addressed
through predator control programmes.
35 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
CHAPTER 10. FLATBACK SEA TURTLES
10.1 DISTRIBUTION & MIGRATIONS
The flatback turtle is unique in that is nests only in Australia, with some northward distribution of
foraging grounds. Foraging flatbacks have been encountered in neighbouring Papua New Guinea
and Indonesia but no nesting records for this species exist in those countries. It is presumed that
flatbacks also forage in waters of Timor-Leste (Figure 10-1, 10-2). Of relevance to the flatback
populations in the ATS region are the Arafura Sea / Gulf of Carpentaria / Torres Strait flatback
turtles, where the largest nesting sites for flatbacks include Crab Island, Deliverance Island and
Kerr Island in the east; and the flatback turtles nesting at Cape Dommet in Western Australia and
those nesting down to the Kimberly Islands. The largest flatback rookery in Queensland is on
Crab Island just off the Northwest coast of Cape York Peninsula, Australia. Annual nesting
numbers were reported as ~1,000 to 2,000 female turtles a year (Commonwealth of Australia
2017). However, this is likely a gross underestimation given recent studies by Leis (2008), who
recorded 6,684 nesting events between August 27 and September 27, 2008. Deliverance Island
(Warul Kara) hosts ~100-200 flatback turtles annually (Hamann et al. 2015). Between ~600 and
~1,000 nests are also laid in the Jardine River rookery, equating to some 200 to 500 annual
breeders (Freeman et al. 2015). Limpus et al. (2016a, 2017a) recorded over 500 flatback clutches
on Mapoon beaches in 2016, and over 600 clutches in 2017, highlighting the importance of these
western Cape York peninsula beaches for flatback turtles.
Figure 34. Flatback turtle distribution in the ATS region. Darker colours indicate greater number of records per
1o cells. Image source: OBIS-Seamap 2021
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 36
In the Northern Territory, flatback Turtles were recorded nesting all around the coast, on both
mainland and on islands (Chatto & Baker 2008). Some 1,600 nests were recorded between 1991
and 2004 on islands, while mainland beaches recorded only ~200 (Chatto & Baker 2008).
Flatbacks have been recorded nesting on nearly every Northern Territory beach where marine
turtle nesting was confirmed, regardless of whether or not other species also nested at that
location. Cape Domett supports one of the largest nesting flatback turtle populations with
annual abundance in the order of several thousand individuals (estimated = 3,250, 95% CI = 1431–
7757; Whiting et al. 2008). In the Kakadu National Park, Groom et al. (2017) calculated the number
of flatbacks to be between 97 and 183 turtles per year with no significant trend over 12 years of
monitoring. At Bare Sand Island, the estimated total number of turtles varied from 54 to 160
between 1996 and 2020, with no signs of population size change (Guinea 2020).
Western Australia also supports substantial flatback turtle nesting accounting for approximately
one third of the total nesting flatbacks in Australia. There are two genetic stocks of flatback turtles,
of which the northern stock, which breeds mainly at Cape Domett and presumably adjacent areas
in western Arnhem Land (FitzSimmons et. al. 1996; Dutton et. al. 2002), is most pertinent to the ATS
region. The southern stock, which nests throughout the Northwest Shelf from Exmouth to about
the Lacepede Islands is linked to the ATS region via migratory data, with numerous Western
Australian turtles foraging, and migrating through, in the Timor and Arafura Seas.
Figure 35. Flatback turtle distribution in the northern Australian region. Image source: Australia Species Profile
and Threats Database, Accessed May 26, 2021
Due to their non-oceanic nature, whereby flatback turtles are restricted to Australian waters and
those of southern Papua New Guinea and Indonesia, the migration and habitat connectivity data
for this species is limited mostly to the Australian continental shelf and the Timor Sea. Flatbacks
from the Lacepede Islands forage in the Timor Sea in average water depths of 74 ± 12 m, 135 ± 35
km from the Australian shore (Figure 33; Thumbs et al. 2017). Movements of post-nesting female
37 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
flatbacks from Torres Straits all oriented to the west into the Arafura and Timor Seas and not to
the east (Figure 10-4; Hamann 2015). Thums et al. (2018) also recorded movements of 35 flatback
turtles from Bells Beach, ~38 km northeast of Karratha, and Delambre Island, ~18 km north of
Bells Beach moving northeast into the Timor Sea (Figure 35).
Figure 36. Flatback turtle dispersal from the Lacapede Islands in Western Australia. Image source: Adapted
from Thums et al. 2017
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 38
Figure 37. Migration routes and foraging areas for five female flatback turtles after nesting at Warul Kawa in 2013
(left) and six female flatback turtles after nesting at Warul Kawa in 2014. Image source: Hamann et al. 2015
Figure 38. State-space model position estimates of flatback sea turtles from Western Australia. Tracks are
coloured by behavioural mode: yellow: inter-nesting; blue: outward transit; red: foraging; green: other transit.
Image source: Thumbs et al. 2018
A comprehensive analysis of flatback movements from Western Australia was compiled by
Poutinen & Thums (2016), that identified seven key foraging areas for flatbacks in the Timor Sea,
five onshore and two offshore (Figure 36). The study reported that turtles spent the most time in
the inshore hotspot #5 (Cape Leveque; Figure 36), while the most individual turtles were
39 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
recorded by far in inshore hotspot #4 (Lacepede Islands; Figure 36). While these two sites are
outside of the ATS region, four other hotspot areas are within the Timor Sea and a large
proportion of movements were recorded in the Timor Sea also (grey lines, Figure 36).
Figure 39. Post-nesting dispersal of flatback turtles showing the seven foraging area hotspots across NW
Australia shown at a 2 km pixel scale. Image source: Poutinen & Thums 2016
Flatback turtles from the large rookery at Cape Domett also disperse widely across both the
Arafura and Timor seas (Figure 37; Whiting et al. unpublished data). However, they appear to
remain in shallow (<100m) waters on the Australian continental shelf (see also Figure 21).
Figure 40. Dispersal of post-nesting flatback turtles from Cape Domett, NT: S. Whiting et al., unpublished
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 40
10.2 GENETIC STRUCTURE
The flatback turtle only breeds in Australia but has migrations that can include international
waters. The most comprehensive assessment of genetic structure of flatback turtles in Australia
is presented by FitzSimmons et al. (2020). One predominant haplotype was found across all
rookeries, but other haplotype groups were regionally specific, across 17 main rookeries (Figure
10-6; FitzSimmons et al. 2020). This study led to the identification of seven genetic stocks, with
geographic boundaries of rookeries used by genetic stocks varying from 160km to 1,300km
(Figure 37). Genetic divergence was consistently higher between the eastern Queensland
rookeries and all other rookeries, highlighting the genetic distinction of the flatback turtles in the
east from other flatbacks across the north and west of Australia.
Figure 41. Distribution of the nine most common mitochondrial DNA haplotypes, and combined ‘other’
category, sampled from 17 flatback turtle (Natator depressus) rookeries. Image source: FitzSimmons et al.
2020
FitzSimmons et al. (2020) noted that discontinuities in haplotype frequencies among rookeries
may reflect historical patterns of low-frequency colonization events by small numbers of
turtles, followed by strong rookery fidelity of those turtles, and later fidelity of their offspring
to natal regions for breeding. If so, observed patterns suggest that colonisation events do not
necessarily involve turtles from nearby rookeries, as seen in the discontinuous distribution of
some flatback haplotypes.
41 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
Figure 42. Designated flatback turtle (Natator depressus) genetic stocks based on the analyses of 17 rookeries
across their range. Image source: FitzSimmons et al. 2020
10.3 POPULATION TRENDS
Long-term trends are available for only a handful of sites in Australia. Groom et al. (2017)
conducted a long- term capture-mark-recapture program on nesting flatback turtles on Field
Island in Kakadu National Park, a World Heritage Area that is jointly managed by Aboriginal
landowners and the Australian Government, from 2002 to 2013, and determined there was a nonsignificant trend over 12 years of monitoring (Figure 40). This is mirrored by long-term data for
Bare Sand Island from 1996 to 2020 (Figure 41, Guinea 2020).
Figure 43. Nesting abundance of flatback turtles (Natator depressus) at Kakadu National Park, NT. Image
source: Groom et al. 2017
.
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 42
Figure 44. Nesting abundance of flatback turtles (Natator depressus) at Bare Sand Island, NT. Image source: M
Guinea, 2020
43 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
CHAPTER 11. THREATS
Given the lack of a complete understanding of the magnitude of impacts on sea turtle
populations, it is not possible to accurately identify the highest and lowest priority threats. For
instance, while climate change may impact sea turtle populations, it is currently unknown to what
extent this occurs. While fishery bycatch in Australia may be well managed, this is less so outside
of Australian waters, and it is likely (as shown below) that thousands of sea turtles are lost to
fisheries each year. Given these uncertainties, the threats listed below are not presented in any
order of priority but are believed to be far higher priority than some other threats such as vessel
strikes, oil pollution, and coastal development, which are not discussed herein.
11.1 BYCATCH IN FISHERIES
Fisheries in the ATS region include those managed by Australia, Timor-Leste, Indonesia and PNG
as well as foreign vessels that may be operating under the flags of these and other countries
(Wagey et al. 2009, Williams 2007). Indonesia is the highest contributor to the fisheries sector
with ~250,000 fishers, followed by Timor-Leste with ~5,000 fishers and Australia with ~650
fishers (ATSEA 2011). Key fisheries include the Arafura Sea shrimp trawl fishery in Indonesia (the
Arafura Sea shelf area between West Papua and Australia is shallow and hosts trawling for
penaeid shrimps), deep water large-scale purse seines and artisanal pole-and-line, trolling gear
and mini-seines that catch small pelagic fishes, tuna and skipjack, often using FADS (fishing
aggregating devices). In Australia the Northern Prawn Trawl Fishery in Australia, the Torres Strait
Prawn Fishery (TSPF), the Kimberley Prawn Fishery (KCPF) and the Northern Territory pelagic
gillnet fishery are implicated in bycatch of ATS region turtles, albeit at low levels given the use of
Turtle Excluder Devices.
In Australia significant steps have been taken to reduce fishery-turtle interactions. The
introduction of turtle excluder devices (TEDs) in trawl fisheries has reduced turtle mortalities
when used correctly, with fewer captures since 2001, and with the majority being released alive
(Brewer et al. 2006). For example, in 1999, 780 turtles were caught and released by the Northern
Prawn Fishery, with 96 turtle deaths. In 2006, following the introduction of turtle excluder
devices, 31 sea turtles were caught and all were released alive (DEWA 2008). In addition, the use
of de-hookers and line cutters in long-line fisheries has also improved marine turtle survival as
they facilitate the live release of turtles captured on gear (Patterson et al. 2015).
However, there are still some areas where fishery-turtle interactions are of concern, as fisheries
continue to interact with turtles (Figure 42). One area is the Gulf of Carpentaria and the Northern
Territory near Darwin and throughout eastern Arnhem Land (Figure 43), where the highest rates
of turtle/fishery interactions have been reported (Riskas et al. 2016). There is concern that the
olive ridley turtle, which has seen large population reductions in western Cape York, may
comprise a large portion of these bycaught turtles (Jensen et al. 2013). Riskas et al. (2016) also
noted that while the bycatch near Darwin could be attributed to the Northern Territory pelagic
gillnet fishery, the reports of turtle bycatch in the Gulf came almost exclusively from the
Northern Prawn Trawl Fishery. They also noted that olive ridley turtles were reported in the
Northern Prawn Trawl Fishery at an average rate of eight turtles per year. They suggested that
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 44
these annual bycatch rates could place proportionally higher pressure on Australian olive ridleys,
which are also threatened by egg depredation and mortality in ghost nets (Jensen et al. 2013,
Limpus 2007e, Wilcox et al. 2013). Given the existence of several different fisheries, with different
reporting avenues and log-book record programmes, Riskas et al. (2015) indicated that the
cumulative impact of all fisheries on any given stock remained unquantified.
Figure 45. Spatial distribution of cumulative turtle interactions with Commonwealth-managed fisheries, 2000–
2013. A: Groote Eyland; B: Sir Edward Pellew Islands; C: Wellesley Islands. Image source: Riskas et al. 2016
Figure 46. Spatial distribution patterns of cumulative turtle interactions with Northern Territory-managed
fisheries, 2000–2013. E: Tiwi Islands; F: East Arnhem Land. Image source: Riskas et al. 2016
45 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
Turtles are also bycaught in Australian gillnet fisheries. As an example, 24 flatback turtles were
estimated to have drowned in a 2,000m bottom set monofilament net shark net over a two-week
period, approximately 4km off-shore in Fogg Bay, Northern Territory in 1991 (Guinea & Chatto,
1992). Similarly, an onboard-observer on a Taiwanese gill net boat off the Arnhem Land coast
recorded seven flatbacks out of 16 turtles captured over approximately a four-month period,
with 81 sets of a 10.5km monofilament net in 1985-86. (Limpus 2007f).
Immature flatbacks are also regularly captured in gill nets set along the coast of the southeastern Gulf of Carpentaria and some of these turtles are drowned (unpublished data, EPA
Queensland Turtle Conservation Project). The annual kill of turtles in the inshore gill net fisheries
of the Gulf of Carpentaria and Arnhem Land remains unquantified.
In Indonesia there is less detailed information on bycatch rates, particularly in the ATS region. One
account of the shrimp fishery in the Arafura Sea in the 1990s indicated that vessels did interact with
turtles, and often did not use the mandated Turtle Excluder Devices. The Directorate General of
Fisheries reported an interaction rate of 7 turtle in 450 hauls for one individual vessel in the 1990s.
At slightly under 1,000,000 hauls per year across the entire fishery, this would equate to a bycatch
of ~15,500 turtles per year in the 1990s. In 2004 there were 338 vessels operating in this fishery
(Purbayanto et al. 2004), which constitutes a 20% to 25% decrease in the number of vessels in the
late 1990s. It is possible then, that the bycatch of turtles has similarly decreased by this proportion,
to ~11,500 to ~12,500 turtles per year. Onboard observations carried out by WWF in 2005 and 2006
in the Arafura Sea, Digul, Kalmana, and Timika fishing areas and reported 133 turtles in only 12
observed vessels in 2005, and in four vessels observed in 2006 an additional 26 turtles were
recorded in just four months (DBC 2014). Interview data from 157 fishermen indicated that an
average of one sea turtle was caught per individual vessel / trip. These estimates are comparable to
the total bycatch estimates presented above and suggest losses of tens of thousands of turtles per
year in the Arafura shrimp trawl fishery.
Indonesia’s assessment of threatened species for the Coral Triangle Initiative (DMCB 2018)
indicated that bycatch in longlines involved primarily olive ridley turtles (78.1% or 490 turtles)
followed by green turtles (7.8% or 49 turtles). All other species were also hooked: hawksbills and
loggerheads (5.3% each equivalent to 33 turtles), leatherbacks (1.9% or 12 turtles) and flatbacks
(1.6%; 10 turtles). The bulk of the longline interactions occurred north of West Papua, north of
Sulawesi and southwest of Java. However, while these interactions occurred outside of the ATS
region it is likely that turtles from the ATS region are implicated in the catches given their
migratory nature. Most turtles implicated in this fishery were reportedly juveniles (DMCB 2018).
WWF-Indonesia and the Directorate of Conservation and Marine Biodiversity (Ministry of Marine
Affairs & Fisheries) indicated in 2015 that the tuna longline industry was unlikely to impact turtles
in the ATS region given most interactions occurred much further west in the Indian Ocean
(DKKLH 2015). Mustika et al. (2014) reported no instances of turtle bycatch in either coastal
gillnets, long lines, and purse seines in Paloh and Adonara in 2013, and it is likely that the
dispersed nature of turtles accounts in part for these findings. Purse seiners in Java indicated
bycatch rates of at least one turtle per trip, especially where the fishing area was near a turtle
nesting beach (DBC 2014).
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 46
Further information on origins of the bycatch, such as through genetic sampling, would be useful
to clarify which turtle populations / stocks are implicated in the industrial fisheries bycatch, much
as was done by Jensen et al. (2013) for turtles caught in ghost nets in northern Australia.
DBMC (2018) also indicate that substantial bycatch occurs in small-scale fisheries: In one WWF
study in Sulawesi an estimated 20 to 30 turtles were caught per vessel per year. Given the vast
numbers of boats operating in the ATS region it is likely that impacts on sea turtles are
substantial – even alarming, should these interaction rates be similar to those in Sulawesi.
Findings at other locations mirrored these high catch rates (Table 11-1). Impacts on turtle species
from small-scale coastal fisheries differ from longlines, which operate in deep waters. In
Kalimantan hawksbill turtles were the most common at ~42% followed by greens (~30%).
Loggerheads, flatbacks and leatherbacks comprised <7% of all bycatch. Gill nets accounted for the
vast proportion of bycatch in small-scale fisheries in Indonesia (Table 2).
Table 1. Estimates of turtle bycatch at a selection of locations in Indonesia. Image source: DCMB 2018
Table 2. Proportion of turtle bycatch by fishing gears in Indonesia. Image source: DCMB 2018
It is likely that small-scale fisheries are a major source of bycatch, particularly those using gillnets.
Additionally, illegal fishing in the ATS region is likely to be substantial, and bycatch from illegal
and unregulated fisheries is likely to be higher than in regulated fisheries. Between 2000 and
2007 there was a two-fold increase in non-motorised vessels, and a five-fold increase in the
number of motorised vessels, particularly in vessels less than 5GT in the ATS region (Edyvane &
Penny 2017). The major increase in fishing activity in the Indonesian EEZ corresponded to a 3-fold
47 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
increase in foreign fishing vessels (legal, illegal) sightings in northern Australian waters. Within
the Australian EEZ, sightings of illegal foreign fishing vessels peaked and reached a maximum in
2005 (6,956 vessels). Numbers then sharply reduced (>80%) following major border control,
surveillance and security operations in the northern Australia in 2005–2006. However, post2007, illegal foreign fishing vessel sightings inside the Australian EEZ increased again (Edyvane
& Penny 2017).
However, there is little in the way of current published statistics that might inform on the
magnitude of turtle bycatch in Indonesian fisheries. This is even less so in Timor-Leste, and this
information gap warrants further attention.
11.2 GHOST NETS
Ghost fishing is defined as the ability of fishing gear to continue to fish after all control of that
gear is lost. This definition however, does not give specifics on how to identify mortality rates
associated with ghost fishing. Ghost nets are of concern in the Arafura and Timor Seas given
the high number of turtles entrained in these nets annually. Materials are transported into the
gulf by southeast trade winds. These winds become northwesterly during the monsoon season
(Wilcox et al. 2013). After this, a clockwise gyre current centred northwest of Groote Eylandt,
exacerbates the problem of ghost nets in the region as it can prohibit ghost nets from escaping
the region (Gunn et al. 2010). Thus, derelict nets in the Gulf become locked into an extended
period of ‘ghost fishing’ until they are washed ashore (White 2003). Since the early 2000s,
Australia’s sparsely populated, remote northern shores have reported very high levels of
foreign, fishing-related marine debris (Edyvane & Penny 2017). Northern Australia has some of
the highest densities of ghost nets in the world, with up to three tons washing ashore per km
of shoreline annually (Wilcox et al. 2015). The estimated total number of turtles caught from
2005 to 2012 by the ~9,000 ghost nets was between 4,866 and 14,600, assuming nets drifted
for one year (Wilcox et al. 2015). Turtle species found in these nets included flatback (9.9%),
green (13.8%), hawksbill (32.6%), loggerhead (1.1%), and olive ridley turtles (42.5%);
approximately 24% of turtles were unidentified.
Nets with relatively larger mesh and smaller twine sizes (e.g., pelagic drift nets) had the highest
probability of entanglement for marine turtles (Wilcox et al. 2015). During this study, net size was
important, with larger nets having higher catch rates. These results point to issues with trawl and
drift-net fisheries; the former due to the large number of nets and fragments found and the latter
due to the very high catch rates resulting from the net design. However, other nets were also
implicated: catch rates for fine-mesh gill nets could reach as high as four turtles / 100 m of net.
Wilcox et al. (2015) concluded that ghost nets were an important and ongoing transboundary
threat to biodiversity in the Arafura and Timor Seas.
Between 2003 and 2008, a total of 2,305 derelict fishing nets washed ashore in Northern Australia
and of these, 89% were identified of foreign origin (i.e. manufacture), compared to 11% attributed
to Australian fishing vessels or fisheries (Edyvane & Penny 2017). These authors concluded that
industrial foreign and Indonesian-flagged fisheries - particularly, illegal, unreported and
unregulated (IUU) trawling activity - and small-scale Indonesian IUU fisheries (primarily targeting
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 48
shark) in the Arafura Sea were likely the major sources of these nets. The arrival and increase in
derelict nets in northern Australia after 2000 coincided with sharp increases in both industrial
foreign fishing (illegal and legal) and Indonesian small-scale fisheries within the Indonesian EEZ
waters of the ATS region.
While the problem is one faced primarily on Australian beaches, recent genetic studies suggest
that turtles entrained in these nets also originate from neighbouring countries, most likely from
Indonesia, with a small number potentially also coming from Timor-Leste (Jensen et al. 2013).
Solutions to the ghost net problem are complex and involve a wide range of stakeholders (Butler
et al. 2013). These include net manufacturers, fishers, government regulatory agencies, local
communities, conservation agencies and artists and art buyers. Some local communities along
the Gulf of Carpentaria and the Northern Territory indicate the ghost net issue may have
decreased slightly in recent years, but it is unlikely to go away and thus impacts to sea turtles in
the ATS region warrants continued investigation.
11.3 PREDATION
There is an extensive understanding of predation in Australia, where multiple predators impact
turtles and their eggs. Large crocodiles, Crocodylus porosus, are predators of nesting female
flatback turtles and olive ridley turtles. Sutherland & Sutherland (2003) recorded a predation rate
of 1.17 females/week by crocodiles during July 1997 at Crab Island. Predation of flatback clutches
by feral mammals or varanid lizards did not occur at the major island rookeries such as Crab or
Deliverance Islands (Limpus et al. 1989, 1993; Sutherland & Sutherland, 2003), but loss of clutches
to feral pigs along the mainland coast south of the Jardine River was presumed to be ~90%
(Limpus et al. 1993). Whytlaw at el. (2013) recorded an overall level of nest mortality of 40.2% with
pigs being responsible for 93% of nest losses. Foxes also are predators of turtle hatchlings in
Australia where the impact on overall hatchling production can be varied (King 2016). Butcher &
Hattingh (2013) recorded 70% nest predation by introduced red foxes, along with additional
predation by feral cats and wild dogs, and King (2016) recorded a nest predation rate of 26% by
red foxes. Guiliano et al. (2015) also recorded predation by night herons (Nycticorax caledonicus),
and reported that 100% of emerged hatchlings of 14 nests were predated by nocturnal avian
predators within an opportunistic subsample of 35 nests. They point out that this was not total
predation but that the issue of night heron predation required further investigation. Whiting et
al. (2008) noted that feral dogs (Canis lupus dingo) were a predator on Cape Domett, taking at
least one clutch of eggs per night. They also recorded several hundred Nankeen night herons
each night but predation on hatchlings was unquantified. The study also documented large
crocodiles attacking adult nesting turtles and also hatchlings (Whiting et al. 2008).
Introduced mammals are also opportunistic predators upon turtle eggs and include feral pigs
(Sus scrofa) and foxes (Vulpes vulpes), and these predators have caused almost total destruction
of eggs at some rookeries (e.g. areas in Western Cape York are thought to have had predation
levels of ~90% over the last 30 years; Limpus 2007f). While the nesting in this region is primarily by
flatback turtles, low density Olive ridley clutches are laid on the same beaches and both species
are subjected to high rates of egg predation. Almost the entire Olive ridley nesting population for
Queensland occurs in this area of intense egg predation (Limpus 2007e). However, recent pig
49 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
removal programmes have resulted in the near-elimination of this threat at the Mapoon beaches
(Limpus et al. 2017b). Rangers from Cobourg Marine Park suggest around 70-90% of nests are
predated on by dogs and goannas. This site is an important site for olive ridleys and there is a
Cobourg genetic stock of green turtles that could be impacted by the high predation. Surveys in
the Tiwi Islands in 2005 indicated that dogs were still a primary predator of eggs (Whiting et al.
2007a). Limpus et al. (2016a) indicates that egg collection and predation by dogs and varanid
lizards is a problem on Flinders, Back and Mapoon beaches, in the western Cape York peninsula,
particularly following many years of pig depredation. Dogs and to a lesser extent goannas were
the most significant predators of turtle eggs on Flinders Beach (Mapoon) during the 2016 and
2017 breeding seasons (Limpus et al. 2016a, 2017b). However, the 2017 turtle breeding season saw
the lowest clutch loss to predators recorded in any one year since annual monitoring of Mapoon
beaches began in 2004 (Limpus et al. 2017b).
On Crab Island, Rufous night herons, blacked-necked storks, beach stone curlews, silver gulls and
pelicans were observed to either predate on hatchlings directly or were identified by their tracks
around newly emerged clutches (Leis 2008). Similarly on Heron Island, Hopley (2008) reported
that predation of the hatchlings was high, especially by Rufous herons, and that only 6.7% of
hatchlings may have reached the sea. Nocturnal avian predation was also recorded on Bare Sand
Island (Giuliano et al. 2015). Only silver gulls were observed to have predated hatchlings during
the day. There was no evidence of predation by feral pigs, Sus scofa, or native varanids on the
island during the study period. However, of concern, crocodiles were a major predator of
hatchlings. Close to 30 crocodiles were consistently counted on each survey night in 2008 (Leis
2008). Crocodiles congregated in areas where the densest hatching occurred. Crocodiles size
varied from 1m to >6m, with numerous medium to large crocodiles (>3.5m) observed. The
amount of predation witnessed indicates that crocodiles are one of the major predators of
hatchlings on the island (Leis 2008). Southerland & Southerland (2003) also reported crocodile
predation at a minimum rate of one adult flatback per week.
Of concern to leatherbacks that migrate through the ATS region, predation of leatherback turtle
eggs by pigs and feral dogs in West Papua is a grave concern, where clutch loss can reach 40%
(Hitipeuw et al. 2007). Tapilatu & Tiwari (2007) found pig predation rates of 29.3% in Jamursba
Medi along with a lower predation rate by dogs. However, recently improved management
approaches appear to have an effect, nest predation is reducing (Lontoh pers. comm.). In PNG
domestic dogs were the most common predator on eggs, and outside of protected and
monitored areas nest loss could reach 100%. After the introduction of protective bamboo grids in
2006 (Pilcher 2006) the success of clutches was higher than 60%. However, this does not appear
to work with the pig predation, given their size and strength.
Pig predation on nests has also been recorded in Timor-Leste (Eisemberg et al. 2014) and it is
likely that feral dogs and varanid lizards are similarly a problem.
11.4 TRADITIONAL TURTLE TAKE
Sea turtles are protected by law in all four countries bordering the ATS region. However, in
Australia, under Section 211 of the Native Title Act 1993, indigenous people with a native title right
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 50
can legitimately take marine turtles and eggs in Australia for communal, non-commercial
purposes, subject to limited exceptions. Little information is currently available on levels of
Indigenous harvest of marine turtles in the Northern Territory and Queensland waters of the Gulf
of Carpentaria but they are believed to be relatively low in some areas, and worryingly high in
others. In the Torres Strait, a small number of nesting females and eggs used to be harvested
annually from Bramble Cay, Dowar and other islands, which likely consisted of an annual nesting
population of several hundred nesting females (Parmenter 1977, 1978). The current magnitude of
take is unknown.
Historically, an estimated 2,410 (2,050–2,760) turtles (approximately 98% green turtles) were
captured annually from the 14 inhabited islands of the Torres Strait Protected Zone, with the
catch biased to females and the majority being adult and near adult turtles (Harris et al. 1992a,b).
An estimated 4,000 might have been killed annually by islanders across the Queensland Torres
Strait (Harris et al. 1992a,b, Limpus 2007a). While the majority of the turtles from this region
originate from the nGBR breeding unit, there is known movement of turtles from the nGBR into
the Gulf of Carpentaria and thus ghost nets are also likely to be of consequence to turtle stocks
from outside the ATS region. Kennett et al. (1998) estimated that approximately 480 green
turtles were collected annually on the northeast Arnhem coast but current levels of take are
unknown. Tiwi Islanders in the Northern Territory continue to exercise their rights to customary
harvest of sea turtles and anecdotal evidence suggest that green turtles are the main turtles
harvested (Whiting et al. 2007a), however no estimates of annual take are available. On the
Dampier peninsula of northern Western Australia, Morris & Lapwood (2001) recorded a harvest
of 96 green turtles in 2002. Subsequently, Morris (pers. comm. In Limpus 2007a) suggested that
the annual harvest for the Dampier Peninsula area could be about 500 green turtles annually. The
total harvest in the Northern Territory is currently unknown, but is likely to be hundreds to
several thousand, while Western Australia is estimated to be several thousand turtles annually
(Kowarsky 1982, Henry & Lyle 2003).
In Papua New Guinea, within the north eastern area of the Torres Strait Protected Zone, there
was a minimum harvest by the Kiwai people estimated at 953 to 1,363 turtles annually during
1985–1987, of which 94– 98% were green turtles (Kwan 1989, 1991). An independent study based
in Tureture village during 1986 provided a larger estimate (by a factor of 2 or more) of the harvest
by the Kiwai (Eley 1989). As noted above for the Queensland Torres Strait turtles, the majority of
the turtles from this region originate from the nGBR breeding unit and are likely of little
consequence to turtle stocks in the ATS region.
While not sanctioned at the national level, there has been a traditional take of leatherback
turtles in the Kei Islands, Indonesia, for many years (Suarez & Starbird 1996, Suarez et al. 2000).
Suarez & Starbird (1996) monitored the harvest between October and November 1994 and
reported a catch of 23 leatherback turtles by Kei Islanders (six males and 17 females), and
between October 1994 and February 1995 Suarez (2000) found 65 leatherback turtle captures
(both sexes). More recently (Lawalata & Hitipeuw 2005) found that at least 29 leatherback
turtles were hunted in the Kei Islands between November 2003 and October 2004 (18 females
and 11 males). However, the number of turtles taken in this traditional practice has declined,
and recently the number of turtles taken each year is down to only 5-10 (J. Wang, NOAA NMFS,
pers. comm.). WWF-Indonesia, with the support of religious leaders, monitors the traditional
51 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
harvesting and implemented an effective management strategy. In the 5 years since its
implementation in 2017, the number of captures has decreased substantially (from 103 to 22 in a
year, Suprapti pers. comm.).
Legal egg harvests are also significant: In Queensland, a large but unquantified annual egg
harvest across the entire northern region. Much of this harvest occurs in eastern and central
Torres Strait, particularly from Bramble Cay and the Murray Islands, and the small rookeries of
the inner shelf of the nBGR (Limpus 2007a), but traditional egg collection occurs throughout the
Northern Territory and in Western Australia. The majority of the turtles from the Torres Strait
originate from the nGBR breeding unit and are likely of little consequence to turtle stocks in the
ATS region. But eggs taken elsewhere directly impact populations in the ATS region. Flatback
eggs have been gathered by indigenous peoples living adjacent to flatback rookeries across
northern Queensland and the Northern Territory (Limpus et al. 1983, 1989, 2007f). Limpus et al.
(2017b) indicated that collection of eggs on Back Beach (Mapoon was a significant issue in 2017.In
the Groote Archipelago and along Arnhem Land, egg collection generally occurs wherever people
can access the beach, and there are concerns in many areas about unsustainable take from
hunting and collection. The size of the harvest is largely unquantified, but is of concern to many
of the indigenous communities who live throughout the region. There are also many remote
beaches that are inaccessible by road and are a long way by sea for community access where egg
collection is not an issue. Tiwi islanders in the Northern Territory also take eggs of any species of
turtle periodically (Whiting et al. 2007a). An emerging threat has been the use of 4X4 vehicles to
cover large distances and collect eggs, but the extent of this practice also remains unquantified
(Limpus 2007f).
There remains a need to explore the sustainability of legal turtle and egg harvests in the ATS
region given that many communities target adult turtles and the overall number of turtles taken
in the region remains unknown.
11.5 ILLEGAL TURTLE TAKE
The most glaring problem in assessing illegal turtle take is that it is illegal, and thus goes
unreported and grossly unquantified. In Timor-Leste, illegal turtle harvesting has been reported
as a major issue especially in the recently declared Nino Konis Santana National Park and Marine
Park (Edyvane et al. 2009). Sealife Trust (2018) reported a brisk trade in turtle meat and
ornaments made from tortoise shell in and around Dili. They reported that meat sales were
common in local markets, and indicated that turtle shell parts came from Manatuto, Liquica,
Same, Lospalos, Viqueque and Suai / Zumalai. The study also indicated that products were not
always brought to market, but rather traded at the individual level, confounding any possibly
quantification. In a personal communication to K. Edyvane in 2008, E. Vitorino reported on an
extensive slaughter of turtles (most appeared to be olive ridley) on Jaco Island, where dozens of
turtle carapaces and cooking / processing facilities were found in a cave. Olive ridley, hawksbill
and green turtle shells were presented at homes along the road from Dili to the east of the
country (Dethmers pers. comm., 2012). It is clear from these reports that illegal take of turtles
across a large part of Timor-Leste is ongoing, possibly on a large scale, but currently unquantified.
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 52
In Indonesia all take of sea turtles is technically illegal, but this remains unquantified (with the
exception of the traditional take in the Kei Islands and the Bali religious green turtle take). Illegal
take of turtles reportedly declined on Rote Island following awareness programmes and
implementation of local laws (Haning 2019). However, there are no estimates of annual take at
this location. Febrianto et al. (2020) document trade of hawksbill shell in Kupang but similarly no
estimates of annual take are available. Dethmers (2019) report that trade in green sea turtles in
Bali continues, and historically Enu Island (Aru) has been a major source of turtles in this market.
It is likely that illegal fishers operating in the Timor Sea also provide turtles for this trade. DBMC
(2018) also indicate that the trade in meat, carapaces and eggs is still a major activity in traditional
markets in Kei Kecil, Saumlaki, and Southeast Maluku, but no estimates of take are available. A
total take across the Indonesian archipelago of 3,279 turtles per year was reported by Humber et
al. (2014), although it is unclear how this figure was derived. But it is likely this is a gross
underestimate, given that Dethmers (2000) reported an annual take of ~5,000 turtles in the Aru
Islands alone. She estimated that, with the ongoing local exploitation pressure and turtles
migrating to and from other regions, the Aru nesting population would go extinct within the next
50 years (Dethmers and Baxter 2010). Hilterman & Goverse (2005) and Nijman (2019) both
document the ongoing illegal trade in turtle products in south Java, so it is evident that illegal
harvest is ongoing but remains unquantified in the Indonesian ATS region. The lack of
understanding of the magnitude of illegal take warrants further attention, and accurate
assessment of the drivers and spatial distribution and impact level of this activity is needed.
While there was substantial harvest of green and hawksbill turtles in Australia in the past for
commercial purposes, in recent years commercial harvest has not been permitted under any
State or Federal legislation, and there is little documented illegal take of turtles in Australia. A
few cases of illegal ‘traditional’ take have been recorded, although this is uncommon (Limpus,
pers. comm.). As noted above, there is a traditional take of turtles in Australia, but today there is
little or negligible other illegal turtle take in Australia.
11.6 EGG COLLECTION
Unquantified egg collection occurs in Indonesia and Timor-Leste. For instance, Dethmers (2010)
reports egg collection in the Aru Islands, and Edyvane et al. (2009) indicate this happens in the
Nino Konis Santana Marine Park in Timor-Leste, but no estimates of annual take are suggested.
Sealife Trust (2018) reported the sale of turtle eggs in and around Dili and noted that the practice
was common but again did not indicate how many clutches may be implicated on an annual basis.
Eisemberg et al. (2014) reported egg collection west of Dili and indicated nesting in the areas was
infrequent (<5 nests) but year-round. It is likely that egg collection occurs throughout the
Indonesian islands to some extent, and on many - if not all - nesting beaches in Timor-Leste, and
further investigation of this activity is warranted.
53 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
11.7 CLIMATE IMPACTS (STORMS, TEMPERATURE, EROSION)
Climate impacts can have multiple effects on sea turtles (e.g. Witt et al. 2010, Fuentes et al. 2013,
Santandrián-Tomillo et al. 2009). Increased storm frequency can exacerbate erosion of nesting
beaches. Sea level rise can lead to shallower beaches, or the loss of beaches altogether.
Increased temperatures can lead to feminisation of stocks. Some studies suggest sea turtle
ranges may be expanding due to climatic changes (e.g. Pike 2013), but caution is warranted in
assuming this will be beneficial (e.g. through increased access to alternate habitats). As Pike
(2013) points out, “some species may be able to disperse successfully to novel areas in an
attempt to access critical resources eroded by climate change, which could allow persistence in
changing environments”; “Other species will have difficulty shifting their ranges because of
limitations imposed by dispersal behaviours (which could limit movements, and thus constrain
the exploration and colonization of novel areas), life history (e.g., repeated use of fixed resources
through time), or because the novel habitat does not contain sufficient resources necessary for
survival or reproduction“. In the case of sea turtles, it is likely that they have adapted
evolutionarily to shifting habitats, but it is unknown if the current rate of change is one sea
turtles can adapt to (e.g. Pilcher et al. 2015).
Extreme weather patterns might also profoundly impact sea turtles during El Nińo Southern
Oscillation (ENSO) events. Recent investigations indicated that reproductive success declined in
leatherback sea turtles, and suggested these events could become more frequent in the future
(Santandrián-Tomillo et al. 2015). Contrastingly, storm frequency along the Australian coast was
projected to decrease (Fuentes & Abbs 2010) adding resilience to turtle rookeries, and this
suggests that impacts of storms will be localised and varied. Some places may experience violent
storms and survive, while others may be exposed to less harmful storms but be lost to turtles.
Erosion from major storm events is a concern, and Hitipeuw et al. (2007) describe conditions
through which up to 45% of leatherback nests in West Papua, Indonesia, could be lost to erosion
during the monsoon season. On the Tiwi Islands in Australia’s Northern Territory, surveys after
Cyclone Ingrid in 2005 showed that the beach was eroded substantially causing loss of nests but
no large-scale change to nesting conditions for future nesters. Almost all nests laid eight weeks
prior to Cyclone Ingrid were deemed to have been destroyed (Whiting et al. 2007a).
Rising sea levels is also of concern (e.g. Patino-Marquez et al 2014) as this raises the potential to
significantly increase beach inundation and erosion (Pike et al. 2015). Nest site selection may also
be impaired under less favourable conditions (e.g. Comer Santos et al. 2015), given turtles use a
combination of cues to find nest sites, such as higher elevations and lower sand surface
temperatures.
Global warming patterns may also impact sea turtles. Feminisation of stocks is of concern, and a
recent study pointed to a 97% female bias in turtles from Australia’s largest green turtle rookery
(Jensen et al. 2018). In this study they determined that turtles originating from warmer northern
Great Barrier Reef (nGBR) nesting beaches were extremely female-biased (99.1% of juvenile, 99.8%
of subadult, and 86.8% of adult-sized turtles) and suggested that Australian green turtle rookeries
had been producing primarily females for more than two decades and that the complete
feminization of this population was possible in the near future. Sand temperature monitoring at
Flinders Beach in Mapoon has shown that virtually all olive ridley and flatback offspring in 2015
were likely to be female based on the proportion of time the nests spend above pivotal
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 54
temperatures (Limpus et al. 2016b). Laloë et al. (2015) also detected female biased production of
Green and Hawksbill turtles and projected that this would increase with rising temperatures in the
future. In the Central West Pacific, Summers et al. (2018) documented reduced hatching success
and embryonic death above 34oC in the Mariana Islands, and demonstrated that these impacts, in
combination with egg poaching, could decrease nester abundance.
However, negative temperature effects may not be applicable to all species, as Howard et al.
(2014) found that Flatback turtle embryos were resilient to the heat of climate change. They also
recorded an unusually high pivotal sex-determining temperature in flatback turtles relative to
other sea turtle populations, with an equal ratio of male and female hatchlings at 30.4°C. The
authors suggested that this adaptation might allow some flatback turtle populations to continue
producing large numbers of hatchlings of both sexes under the most extreme climate change
scenarios. Alongside this, Stubbs et al. (2014) also found an anomalous production of male
Flatback turtle hatchlings from Cape Domett (Western Australia).
At present most research on impacts of temperature have focused on nesting turtles and
developing embryos given the ease of access. Chaloupka et al. (2007) demonstrated that
loggerhead turtle nesting abundance in stocks from Australia and Japan decreased following
warmer sea surface temperatures. They suggest the warmer waters may lead to reduced ocean
productivity and that this could lead to long-term declines in loggerheads following protracted
temperature increases. Rising temperatures may also impact hatchling fitness, as elevated
water temperatures were found to decrease swimming performance in green turtles (Booth &
Evans 2011). Little is known of impacts of temperature on other life stages, and this warrants
further investigation.
Raine Island, the world’s largest green turtle rookery, in the nGBR and a source of green turtles
to the Gulf of Carpentaria / Arafura Sea, presents a good case study for predicted impacts of
climate change: Back in 2008 increasing temperatures were projected to alter the sex ratios of
turtle hatchlings and increase heat stress on turtles (Hopley 2008). This was later supported via
research on sex ratios from the nGBR by Jensen et al. (2018) and Booth et al. (2020). It was
predicted that sea level rise may not necessarily result in island erosion and that Raine Island may
become even more unstable and respond to any changes in wind patterns. Erosion was later
found to be a major problem in East Island, Hawaii, in 2018 when the entire island was lost to
Hurricane Walaka. Similarly, Hopley (2008) predicted a sea level rise that would cause a rise in the
water table increasing the risks of turtle nest flooding, and that sea level rise and temperature
increase might change the ecology of the reef flat and delivery of sediment to the island. In the
intervening years the Australian government has invested ~8 million AUD in trying to restore
sand where it was lost, and to raise the sand level so that nests would not be inundated. Hopley
(2008) also suggested El Niño Southern Oscillation (ENSO) events would have important
influences on the breeding behaviour of turtles, and research by Santandrián-Tomillo et al. 2007
supports this prediction.
In short, climate has the potential to decrease reproductive output; to decrease nester
abundance; to alter a species’ distribution and nesting seasonality; to erode or cause the loss of
entire nesting beaches; and to impact sex ratios of emerging turtles. On the other hand, sea
turtles also possess evolutionary traits that have enabled them to adapt to these climatic
changes over time: sea levels have gone up and down by more than 5m repeatedly in the last
55 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
100,000 years, and the planet has warmed and cooled repeatedly during the same period – sea
turtles would surely have gone extinct had they not been able to adapt to these changes. Of
concern, and worthy of recall, are two key issues: 1) turtles adapted to these changes in the
absence of incremental human pressures; and 2) the rate of change today is roughly four times
faster than anything experienced in the past. It is unknown what long-term impacts these two
confounding factors will have on the viability and resilience of sea turtles in the ATS region.
11.8 LIGHT POLLUTION
Artificial light can be responsible for misorientation and disorientation in sea turtle hatchlings
resulting in hatchlings moving away from the ocean and towards brighter light sources (Salmon
et al. 1992, Witherington & Martin 1996). As hatchlings crawl to the ocean they have a primary
tendency to orient away from a darker horizon (typically the darker rear beach dune silhouette,
particularly when envisioned from hatchling eye height ~5-10 mm above the ground) and towards
the brightest horizon, typically the ocean illuminated by the moon and/or stars. The presence of
bright omnidirectional light, such as sky glow caused by anthropogenic light sources, or bright
overhead moonlight coupled with low cloud cover, can disrupt hatchling sea-finding behaviour,
causing disorientation (moving in random directions) and misorientation (orientation in the
wrong direction), which can in turn affect hatchling survivorship. Sky glow (the incremental
overhead brightness caused by urban centres and industrial facilities) has the potential to impact
hatchling orientation, as do point-source lights directly visible from marine turtle nesting
beaches. Point source lights typically attract hatchlings toward the brighter lights
(misorientation), whereas sky glow typically causes general mass disorientation, where
hatchlings roam in random patterns. Both of these effects cause hatchlings to remain on the
beaches for unnaturally longer periods, increasing risks of predation and dehydration, and
causing unnecessary energy expenditure. In extreme cases hatchlings may fail to reach the
ocean, and even once at sea- may continue to be disoriented (Wilson et al. 2018).
Our understanding of regional impacts of anthropogenic light on sea turtles comes from only a
handful of studies in Australia, and the few studies that do exist are conducted mostly as
academic exercises or to detect impacts from major industries. There are no empirical studies of
lighting impacts in the ATS region, but artificial light has been shown to disrupt natural night
horizons in proximity to nesting beaches (Limpus & Kamrowski 2013). Lighting was found to
impact flatback turtle orientation at Curtis Island, where multiple large industries are located.
Hatchlings displayed disrupted sea-finding ability, with light horizons from the direction of nearby
industry significantly brighter than from other directions. The sea-finding disruption observed at
Curtis Island was less pronounced in the presence of moonlight (Kamrowski et al. 2014).
However, Pendoley (2014) also investigated hatchling sea-finding in relation to light levels at the
same location and determined that “flatback and green turtle hatchlings emerging from clutches
located on the primary dune at both Curtis and Facing Islands orientated successfully toward the
ocean without detectable disruption”.
This reported lack of impacts by anthropogenic lighting may be explained in part by the influence
of cloud cover and lunar illumination, which have influenced hatchling orientation through
history. Vandersteen et al. (2020) demonstrated that up to 80% of variation in nigh-time
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 56
brightness was explained by the percentage of moon illuminated, moon altitude, and cloud
cover. That is, anthropogenic lighting is not the only lighting that sea turtles are subjected to.
While individual turtles and hatchlings may be exposed to and impacted by light, at present at the
population level this does not appear to be a problem. Indeed, at all major global nesting sites
where lighting has been a cause of concern, populations all appear to be stable or on the rise (with
the understanding that these turtle populations are also under considerable conservation and
management). At the greater population level, Kamrowski et al. (2012) concluded that despite the
broad geographic scale of impact, the majority of marine turtle nesting sites in Australia appeared
minimally affected by light pollution exposure. However, it is worthy to note that our population
level observations or today are of nesting adults and therefore the data we are considering here
may actually be reflective of the hatchling light environment of 20-30 years ago.
Thums et al. (2016) investigated attraction of turtle hatchlings to stationary light sources (such as
navigation beacons and jetty lights) and found that artificial lighting affected hatchling
behaviour, with 88% of individual trajectories oriented towards light sources and spending, on
average, 23% more time in a delineated area (19.5 ± 5min) than under ambient light conditions
(15.8 ± 5 min). This study indicates that light can impact turtles even once they have entered the
sea. On Heron Island turtle hatchlings were also disoriented, particularly on moonless nights,
when 66.7% of tracking trials recorded hatchlings returning to shore, attracted by land-based
light sources (Truscott et al. 2017).
Lighting associated with oil and gas facilities and coastal and island developments may have the
potential to disturb the nesting regimes of sea turtles. On the North West Shelf in Western
Australia, lighting from industrial complexes has been shown to affect flatback, green and
hawksbill turtles (https://www.environment.gov.au/biodiversity/publications/national-lightpollution-guidelines-wildlife). In Western Australia, preliminary results of an investigation into the
impact of flares and facility lighting suggest that impacts are determined by the phase of the
moon, with disorientation greatest in the new moon nights. Another factor is the brightness and
wavelength of the light sources. However, these reports should be interpreted with caution:
ongoing studies at some of these locations do not find impacts from lighting at the population
level – while a handful of hatchlings may be implicated in disorientation, the vast majority of
hatchlings where light is managed all reach the sea, and there are examples of where light is not
managed impacting significant numbers of hatchlings (Limpus 2020).
Given nesting beaches adjacent to the ATS region are predominantly located in isolated areas
where lighting and flares associated with oil and gas facilities are virtually absent, impacts to
turtles on land currently unlikely to be of concern (DAWE 2008). However, as demonstrated by
Thums et al. (2016), offshore lighting can impact sea turtles and there is a potential impact from
deep-water oil and gas exploration in the Timor Sea. However, the magnitude of this impact is
hard to predict, given the Thums et al. (2016) study looked at hatchling orientation and it is
unknown if hatchling sea turtles are concentrated in areas where rigs and offshore facilities are
located. Further investigation into this potential impact is warranted.
57 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
CHAPTER 12. LEGAL INFRASTRUCTURE
12.1 NATIONAL LEGAL PROVISIONS
In Australia all species of sea turtles are protected via the Environment Protection and
Biodiversity Conservation Act (1999) and via state/territory government legislation: The Northern
Territory Parks and Wildlife Conservation Act (2014), the Queensland Nature Conservation Act
(1992), and the Western Australian Wildlife Conservation Act (1950). Turtles may be legally
hunted by Aboriginal and Torres Strait Islander people under section 211 of the Native Title Act
1993 for personal, domestic or non-commercial communal needs.
In Indonesia all species of sea turtles are protected via Government Regulation No. 7 (1999). In
addition, there is the Bali Governor Decree No. 243 (1999) that revoked the green turtle take
permit for religious festivals, and Act No. 5 /1990 concerning conservation of living resources and
their ecosystems provides prohibition for and sanction of direct harvest of protected species.
In Papua New Guinea only the leatherback turtle is protected via the Fauna (Protection and
Control) Act (1976).
In Timor-Leste all species of sea turtles are protected via the United Nations Transitional
Administration in East Timor (UNTAET) Regulation No. 2000/19.
12.2 RELEVANT INTERNATIONAL CONVENTIONS
Australia, Indonesia, Papua New Guinea and Timor-Leste are all contracting parties to the
Convention on Biological Diversity (CBD).
Australia, Indonesia, and Papua New Guinea are contracting parties to the Convention on
International Trade in Endangered Species of Wild Fauna and Flora (CITES).
Only Australia is a Party (since 1991) to the Convention on Migratory Species (CMS). However,
Australia (2001), Indonesia (2005) and Papua New Guinea (2010) are Signatories to the CMS
Memorandum of Understanding on the Conservation and Management of Marine Turtles and
their Habitats of the Indian Ocean and South-East Asia (IOSEA MoU).
Australia, Indonesia, and Papua New Guinea are contracting parties to the Ramsar Convention on
Wetlands of International Importance especially as Waterfowl Habitat (RAMSAR).
12.3 FISHERIES MANAGEMENT
In Australia, three key commercial fisheries that may interact with sea turtles include the Torres
Strait Prawn Fishery managed under the Torres Strait Prawn Fishery Management Plan 2009, the
Northern Prawn Trawl Fishery managed under the Northern Prawn Fishery Management Plan
1995 (amended 2012), and the North West Slope Trawl Fishery (NWSTF), managed under the
North West Slope Trawl Fishery and Western Deepwater Trawl Fishery: statement of
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 58
management arrangements (AFMA 2012). There is a turtle fishery in the Torres Strait managed
under the Torres Strait Fisheries Act 1984 and Fisheries Management Notice No. 66. This is also a
commercial fishery but is managed by States and Territories rather than the Commonwealth.
There are also multiple coastal fisheries using hook & line, gillnets, traps and other gears across
all of the northern Australian region that can potentially interact with turtles. In Queensland
these are governed under the Fisheries Act 1994, the Fisheries (General) Regulation 2019, the
Fisheries (Commercial Fisheries) Regulation 2019, the Fisheries Declaration (2019) and the
Fisheries (Quota) Declaration 2019. In the Northern Territory fisheries are governed under the
Territory of Australia Fisheries Act 1988 and the Northern Territory of Australia Fisheries
Regulations 1993. In Western Australia fisheries are governed under the Fish Resources
Management Act 1994, the Pearling Act 1990, the Fisheries Adjustment Schemes Act 1987, the
Fishing and Related Industries Compensation (Marine Reserves) Act 1997, and the Fishing
Industry Promotion Training and Management Levy Act.
In Indonesia fisheries are managed by Fishery Management Areas, two of which are included in
the Arafura and Timor Seas. Fisheries are regulated nationally via the Law 31 (2004), amended by
Law 45 (2009) covering fisheries, license and vessel registration, management of IUU and
destructive fishing, standardization of fish processing, tax, and conservation as well as estimation
of the potency of fishery resources in the Fisheries Management Areas. There is also Law 27
(2007) as amended by Law 1 (2014) regarding management of coastal areas and small islands;
Law 32 (2014) regarding maritime surveillance, management and harmonization among marine
stakeholders; Law 7 (2016) regarding protection and empowerment of fishermen; Government
Regulation 60 (2007) regarding conservation of fishery resources: Ministerial Decree 47 (2016)
regarding total allowable catch and utilization rate of fishery resources; and Ministerial Decree
75-85 (2016) establishing fisheries management plans.
In Papua New Guinea the Fisheries Management Act (1998) and Fisheries Management
Regulation (2000) regulate the set-up of the National Fisheries Authority, the supervision of
pelagic fisheries, and local and species-specific fisheries management plans.
In Timor-Leste, laws and ministerial edicts governing fishery-related policy include Decree No.
5/2000 (General Regulation on Fishing); Decree-Law No 6/2004 (General basis of the legal regime
for the management and regulation of fisheries and aquaculture); Ministerial Order
06/42/Gm/Ii/2005 (Sanctions for fisheries infringements); Ministerial Order 04/115/Gm/Iv/2005 (List
of protected aquatic species); Ministerial Order 03/05/Gm/I/2005 (Percentages Of Bycatch);
Ministerial Order 02/04/Gm/I/2005 (Main fisheries); Ministerial Order 01/03/Gm/I/2005 (Definition
of fishing zones); Ministerial Order 05/116/Gm/Iv/2005 (Minimum size and weight of capture
species); Ministerial Order 06/42/Gm/Ii/2005 (Fines for fishing infractions); and Decree-Law
21/2008 (Implementation of the satellite system for monitoring fishing vessels).
12.4 INDIGENOUS COMMUNITY MANAGEMENT
In Australia, under Section 211 of the Native Title Act 1993, indigenous people with a native title
right can legitimately hunt marine turtles for communal, non-commercial purposes. In recent
decades numerous indigenous communities across northern Australia have declared dedicated
59 | STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS
Indigenous Protected Areas (IPAs) over their traditional land and sea Country and developed
traditional land IPA management plans (sometimes known as Healthy Country Plans in the
Northern Territory and Working on Country Plans in the Torres Strait). It is also worth noting that
some Indigenous groups have agreed to put in place arrangements, e.g. in their IPA and Healthy
Country Plans or in State/Territory/Regional plans, limiting or preventing the hunting of marine
turtles or particular marine turtle species. These plans are built on customary practices and
reflect the aspirations, customs, traditions and history of the traditional owners of the land. Sea
turtles are sacred to all of these communities, and feature prominently in the Healthy Country
Plans, where issues related to sustainability of turtle use are a key feature.
In Timor-Leste there exists a local resource management l ban called Tara bandu, which is a
traditional community-based resource management mechanism. Tara bandu is a traditional
Timorese custom that enforces peace and reconciliation through the power of public agreement.
Tara bandu involves handing of culturally significant items from a wooden shaft to place a ban on
certain agricultural or social activities within a certain area.
Sasi is a local traditional resource management system, used in Central Maluku and akin to TimorLeste’s Tara bandu. It implements spatial and temporal prohibitions on harvesting or gathering
resources from the tidal zone or marine territory of a village.
STATUS OF SEA TURTLES IN THE ARAFURA AND TIMOR SEAS | 60
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