CCSBT-ESC/0609/Info 01 Examining the movement and residency of adult SBT in the Tasman Sea and on their spawning grounds south of Indonesia using pop-up archival tags J.S. Gunn K. Evans T.A. Patterson T.I. Carter Prepared for the CCSBT 7th Meeting of the Stock Assessment Group (SAG7) and the 11th Meeting of the Extended Scientific Committee (ESC11) 4-11 September, and 12-15 September 2006, Tokyo, Japan CCSBT-ESC/0609/Info01 Short Abstract to be provided Pop-up Satellite Archival Tags (PSATs) were deployed on 51 large (156–200cm length to caudal fork) southern bluefin tuna (Thunnus maccoyii) in the western Tasman Sea during the austral winters of 2001-2005. Southern bluefin tuna (SBT) were resident in the Tasman Sea for up to six months, with movements away from the tagging area occurring at highly variable rates. In general, SBT moved south into the Southern Ocean, west along the southern continental margin of Australia and then into the Indian Ocean. Three individuals moved east into the central Tasman Sea, with one individual reaching New Zealand waters before returning to the western Tasman Sea. We describe the first observed migration of a SBT from the Tasman Sea to the Indian Ocean spawning grounds south of Indonesia. Individuals spent most of their time on the continental shelf/slope region with an estimated 84 % of time spent in the Australian Fishing Zone. While inconclusive, movement data presented here raise the possibility that SBT estimated to be recruited to the spawning stock are not obligate annual spawners. In general, SBT demonstrated a distinct preference for temperatures between 18-20°C, adjusting depth preferences to reflect changes in the vertical distribution of their thermal preferences. Individuals demonstrated periods of distinct diurnal diving patterns and periods where swimming depths were adjusted to remain at a constant light level over the course of a day. These new data are a significant advance toward greater understanding the spatial dynamics of large SBT and understanding the connectivity between distant regions of their distribution. KEYWORDS: Southern bluefin tuna, Pop-up Satellite Archival Tag, spawning migration, spatial dynamics, habitat preferences. 1 Examining the movement and residency of adult SBT in the Tasman Sea and on their spawning grounds south of Indonesia using pop-up archival tags John Gunn Karen Evans Toby Patterson Thor Carter Final Report to the Department of Agriculture, Fisheries and Forestry July 2006 Examining the movement and residency of adult SBT in the Tasman Sea and on their spawning grounds south of Indonesia using pop-up archival tags J.S. Gunn, K. Evans, T.A. Patterson and T.I. Carter. June 2006 Department of Agriculture, Fisheries and Forestry Final report – DAFF Movement and residency of SBT in the Tasman Sea Published by CSIRO Marine Research Copyright Department of Agriculture, Forestry and Fisheries, Commonwealth Scientific and Industrial Research Organisation (‘CSIRO’) Australia 2006. All rights are reserved and no part of this publication covered by copyright may be reproduced or copied in any form or by any means except with the written permission of the copyright owners. Neither may information be stored electronically in any form whatsoever without such permission. The results and analyses contained in this Report are based on a number of technical, circumstantial or otherwise specified assumptions and parameters. The user must make its own assessment of the suitability for its use of the information or material contained in or generated from the Report. To the extent permitted by law, CSIRO excludes all liability to any party for expenses, losses, damages and costs arising directly or indirectly from using this Report. The use of this Report is subject to the terms on which it was prepared by CSIRO. In particular, the Report may only be used for the following purposes. this Report may be copied for distribution within the Client’s organisation; the information in this Report may be used by the entity for which it was prepared (“the Client”), or by the Client’s contractors and agents, for the Client’s internal business operations (but not licensing to third parties); extracts of the Report distributed for these purposes must clearly note that the extract is part of a larger Report prepared by CSIRO for the Client. The Report must not be used as a means of endorsement without the prior written consent of CSIRO. The name, trade mark or logo of CSIRO must not be used without the prior written consent of CSIRO. Gunn, John S. Examining the movement and residency of adult SBT in the Tasman Sea and on their spawning grounds south of Indonesia using pop-up archival tags. Bibliography. Includes index. ISBN 1 921232 00 5. 1. Bluefin tuna - Monitoring - Australia, Southern. 2. Bluefin tuna - Monitoring - Indian Ocean. 3. Bluefin tuna - Spawning. 4. Fish tagging - Australia, Southern. I. CSIRO. Marine and Atmospheric Research. II. Title. 597.7830994 Front cover design: Louise Bell, CSIRO Marine and Atmospheric Research i Final report – DAFF Movement and residency of SBT in the Tasman Sea Table of Contents 1. NON-TECHNICAL SUMMARY ........................................................................ 1 2. ACKNOWLEDGEMENTS ................................................................................ 4 3. BACKGROUND ............................................................................................... 5 4. NEED ......................................................................................................... 7 5. OBJECTIVES ................................................................................................. 10 6. METHODS ...................................................................................................... 11 6.1. Tagging operations ................................................................................ 11 6.2. Data and analyses .................................................................................. 12 6.2.1. Age classification of SBT ............................................................ 12 6.2.2. PSAT attachment duration .......................................................... 13 6.2.3. Potential mortalities .................................................................... 13 6.2.4. Location estimates ...................................................................... 13 6.2.2. Habitat preferences and behaviour ............................................ 15 7. RESULTS ....................................................................................................... 16 7.1. PSAT attachment duration .................................................................... 16 7.2. Potential mortalities ............................................................................... 17 7.3. Geolocation accuracy ............................................................................ 21 7.4. Migration and residency patterns ......................................................... 21 7.5. Habitat preferences and behaviour ...................................................... 28 7.6. Fine scale habitat preferences and behaviour .................................... 32 7.7 Habitat preferences and behaviour on the spawning ground ............ 36 8. DISCUSSION ................................................................................................. 37 8.1. PSAT attachment duration .................................................................... 37 8.2. Geolocation accuracy ............................................................................ 40 8.3. Migration and residency patterns ......................................................... 40 8.4. Habitat preferences and behaviour ...................................................... 42 8.5. Habitat preferences and behaviour on the spawning ground ............ 44 ii Final report – DAFF Movement and residency of SBT in the Tasman Sea 9. CONCLUSIONS/OUTCOMES ACHIEVED .................................................... 46 10. FURTHER DEVELOPMENT .......................................................................... 48 11. REFERENCES ............................................................................................... 51 12. APPENDICES ................................................................................................ 62 APPENDIX A: Position estimates of SBT tagged in the western Tasman Sea with pop-up satellite archival tags 2001-2005. .......................................... 62 iii Final report – DAFF Movement and residency of SBT in the Tasman Sea 1. NON-TECHNICAL SUMMARY Pop-up Satellite Archival Tags (PSATs) were deployed on 51 large (156–200cm length to caudal fork) southern bluefin tuna (Thunnus maccoyii ) in the western Tasman Sea during the austral winters of 2001-2005. Attachment durations of PSATs on southern bluefin tuna (SBT) ranged 2–206 days and data were received from 46 of the 51 PSATs deployed. Tag attachment durations increased throughout the period of the study largely through improved anchor and tether designs and the implementation of a secondary anchor. However, despite these improvements the single largest hindrance to accumulating long-term data on the movements and habitat preferences of SBT using PSATs in this tagging study was achieving long term attachments. Individual SBT made large scale migrations between separate foraging areas and to the area of the spawning grounds, demonstrating connectivity within the SBT stock over very large spatial scales within