TECHNICAL 77 REPORT 2008 THE DISTRIBUTION AND STATUS OF MARINE TURTLE NESTING IN THE NORTHERN TERRITORY Ray Chatto Bryan Baker Parks and Wildlife Service Department of Natural Resources, Environment, The Arts and Sport 77 TECHNICAL REPORT 2008 THE DISTRIBUTION AND STATUS OF MARINE TURTLE NESTING IN THE NORTHERN TERRITORY Ray Chatto Bryan Baker Parks and Wildlife Service Department of Natural Resources, Environment, The Arts and Sport © Parks and Wildlife Service of the NT PO Box 496, Palmerston, NT, 0831, Australia ISBN 1 920772 72 3. This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without prior written permission from the author. Request and inquiries concerning publication should be addressed to Parks and Wildlife Service of the NT, PO Box 496, Palmerston, NT 0831. Views expressed by the author do not necessarily reflect the views and policies of Parks and Wildlife Service of the NT. Cover photograph: Nesting Green Turtle. Photo Gary Bell. PREVIOUS REPORTS IN THIS SERIES by Ray Chatto WATERBIRD BREEDING COLONIES IN THE TOP END OF THE NT. Technical Report 69/2000 http://www.nt.gov.au/nreta/publications/wildlife/science/pdf/2000_waterbirds_rpt69.pdf THE DISTRIBUTION AND STATUS OF COLONIAL BREEDING SEABIRDS IN THE NT. Technical Report 70/2001 http://www.nt.gov.au/nreta/publications/wildlife/science/pdf/2001_seabirds_rpt70.pdf THE DISTRIBUTION AND STATUS OF SHOREBIRDS AROUND THE COAST AND COASTAL WETLANDS OF THE NT. Technical Report 73/2003 http://www.nt.gov.au/nreta/publications/wildlife/science/pdf/2003_shorebirds_rpt76.pdf THE DISTRIBUTION AND STATUS OF WATERBIRDS AROUND THE COASTAL WETLANDS OF THE NT. Technical Report 76/2006 http://www.nt.gov.au/nreta/publications/wildlife/science/pdf/2006_waterbirds_report76.pdf EXECUTIVE SUMMARY The Northern Territory (hereafter referred to as NT) coast and coastal wetlands are vast and remote, creating particular challenges for documenting wildlife distribution and abundance. Prior to 1990 there had been little systematic or comprehensive attempts to inventory the biodiversity of these systems. From 1990 to 2004 (and incidentally thereafter) numerous aerial and ground surveys were conducted by RC along the NT coastline and throughout the near-coastal wetlands to locate and document the distribution and status of selected wildlife. These surveys focused on aquatic birds (e.g. seabirds, shorebirds and waterbirds), marine reptiles and marine mammals. During this time around 70 000 separate records totalling around 5.6 million individuals were made in the survey area. A series of four reports detailing the distribution and status of the aquatic birds has been completed. This fifth report in the series details records collected on marine turtle nesting. Between 1990 and 2004 in excess of 7 000 records were collected relating to marine turtle nesting around the NT coast. Marine turtles were recorded nesting around much of the mainland coast and on the many islands with sandy beaches. Most of the high density areas were located on offshore islands, with only a few high density sites found on the mainland, where egg predation was generally much higher. Four species of marine turtle were regularly recorded nesting in the NT. These were the Flatback Turtle (Natator depressus), Green Turtle (Chelonia mydas), Hawksbill Turtle (Eretmochelys imbricata) and Olive Ridley Turtle (Lepidochelys olivacea). Nesting densities varied among species at different sites. Of the four marine turtle species to regularly nest in the NT, Flatback Turtles were clearly recorded as the most widespread nesting species. This species nested on nearly all beaches where any marine turtle nesting occurred, either on their own or with other species. Flatback Turtles and Green Turtles were the two most abundant nesting species. The range of Green Turtle nesting was much more geographically restricted (mostly occurring along the eastern NT coast) but where they did nest, they often did so in very high numbers. The combined major sites of Green Turtle nesting in north eastern Arnhem Land are likely to be of international significance. Olive Ridley Turtles were the second most widespread nesting species after Flatbacks, but over most of their range (which included little of the western coast of the NT) they nested 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 nested in nationally significant numbers. Hawksbill Turtles were the least widespread of the four most frequent nesting species. Their nesting was concentrated on islands in north eastern Arnhem Land and around Groote Eylandt. The combined nesting of the major Hawksbill Turtle nesting sites in this area is likely also to be of international significance. Leatherback Turtle (Dermochelys coriacea) nesting was confirmed from only one site (on Cobourg Peninsula) although there are a few anecdotal reports of occasional nesting from a small number of other areas. Although Loggerhead Turtles (Caretta caretta) are recorded in NT waters, they were not confirmed nesting anywhere in the NT. Several parts of the NT coast can now be considered as internationally or nationally important nesting areas for marine turtles. The most important areas located during these surveys are: Turtle Point in Joseph Bonaparte Gulf, Bare Sand and Quail Islands near Darwin, the south west of Bathurst Island, a number of beaches along the northern coastline of Melville Island, the Smith Point area of Cobourg Peninsula, the islands to the north and east of Croker Island, the Goulburn Islands, NW Crocodile Island, many of the outer islands of the numerous island chains off north eastern Arnhem Land, the i mainland coast and islands between Cape Arnhem and Blue Mud Bay, the eastern part of Groote Eylandt and its associated islands and some of the outer islands in the Sir Edward Pellew Group. Most of these sites are on Aboriginal Land. Although some limitations remain due to the largely unsystematic way the data were collected, the outcome of over 15 years of surveys is that the most important areas, and the timing of nesting, have been identified for the four major nesting species of marine turtle in the NT. The collection and collation of this significant number of marine turtle nesting records has provided the baseline information for future research and management of marine turtles across the NT. As with the many other important fauna sites around the NT coast (documented in previous reports in this series), the significant marine turtle nesting sites are still in a fairly unique position. Many of these sites are still not subject to the pressures associated with large human populations. As such, we should be able to be proactive and ensure the long term security of these sites before problems arise rather than have to seek reactive remedies after damage has occurred. The next step in the process to protect the turtles and their nesting habitat in the NT should be to establish monitoring programs for selected sites and the subsequent drafting of management plans/programs for species and areas. These need to link in with other States, the Commonwealth and regional government plans, and work in with other groups such as indigenous rangers in remote coastal communities. The NT’s marine protected areas program and the Commonwealth ‘Work on Country’ programs supporting Indigenous people to manage resources can provide vehicles for such cooperative programs. ii CONTENTS Executive Summary ................................................................................................................................... i Contents ................................................................................................................................................... iii List of Figures ........................................................................................................................................... v List of Tables............................................................................................................................................ ix List of Plates............................................................................................................................................. xi Acknowledgments................................................................................................................................... xv Background and objectives ....................................................................................................................... 1 Study area and environment...................................................................................................................... 3 Methods Nesting data ................................................................................................................................... 5 Mapping coast sections ................................................................................................................ 13 GIS data used ............................................................................................................................... 14 Data Presentation ......................................................................................................................... 14 Nesting activity within marine bioregions .............................................................................................. 19 All NT regions ............................................................................................................................