MMMaaarrriiinnneee EEEnnnvvviiirrrooonnnmmmeeennnttt &&& EEEcccooolllooogggyyy Mitigating Seal Interactions in the SRLF and the Gillnet Sector SESSF in South Australia Final Report to the Fisheries Research and Development Corporation Photo: B. Page (SARDI) SD Goldsworthy, B Page, PD Shaughnessy, A Linnane FRDC PROJECT NUMBER: 2007/041 SARDI Publication No. F2009/000613-1 SARDI Research Report Series No. 405 ISBN: 978-1-921563-26-3 March 2010 Mitigating Seal Interactions in the SRLF and the Gillnet Sector SESSF in South Australia Final Report to the Fisheries Research and Development Corporation by SD Goldsworthy, B Page, PD Shaughnessy, A Linnane FRDC PROJECT NUMBER: 2007/041 SARDI Publication No. F2009/000613-1 SARDI Research Report Series No. 405 ISBN: 978-1-921563-26-3 March 2010 This publication may be cited as: Goldsworthy, S.D., Page B, Shaughnessy, P.D and Linnane A (2010). Mitigating Seal Interactions in the SRLF and the Gillnet Sector SESSF in South Australia. Report to the Fisheries Research and Development Institute. South Australian Research and Development Institute (Aquatic Sciences), Adelaide. SARDI Publication No. F2009/000613-1. SARDI Research Report Series No. 405. Authors: SD Goldsworthy1, B Page1, PD Shaughnessy2 , A Linnane1 1 SARDI, 2 Hamra Avenue, West Beach SA 5024 2 South Australian Museum, North Terrace, Adelaide, SA, 5000 South Australian Research and Development Institute SARDI Aquatic Sciences 2 Hamra Avenue West Beach SA 5024 Telephone: (08) 8207 5400 Facsimile: (08) 8207 5406 http://www.sardi.sa.gov.au DISCLAIMER The authors do not warrant that the information in this document is free from errors or omissions. The authors do not accept any form of liability, be it contractual, tortious, or otherwise, for the contents of this document or for any consequences arising from its use or any reliance placed upon it. 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Information may not be stored electronically in any form whatsoever without such permission. Printed in Adelaide: March 2010 SARDI Publication No. F2009/000613-1 SARDI Research Report Series No. 405 ISBN: 978-1-921563-26-3 Author(s): S.D. Goldsworthy, B. Page, P.D. Shaughnessy and A. Linnane Reviewer(s): M. Deveney, J. Tanner, D. Currie and K. Rodda Approved by: J. Tanner Principal Scientist, Marine Environment & Ecology Signed: Date: 29 March 2010 Circulation: Public Domain Table of contents 3 TABLE OF CONTENTS TABLE OF CONTENTS...........................................................................................................3 1 NON TECHNICAL SUMMARY ..........................................................................................5 2 ACKNOWLEDGMENTS.....................................................................................................8 3 BACKGROUND .................................................................................................................9 AUSTRALIAN SEA LION ..........................................................................................................9 ASL INTERACTIONS WITH THE ROCK LOBSTER FISHERY........................................................11 Background to the rock lobster fishery........................................................................11 ASL lobster-pot interactions ........................................................................................12 ASL INTERACTIONS WITH THE SHARK GILLNET FISHERY........................................................15 Background to the shark gillnet fishery .......................................................................15 ASL interactions with the demersal gillnets.................................................................17 Current spatial management of the shark gillnet fishery .............................................20 COMPARISON OF POTENTIAL IMPACTS OF BYCATCH OF ASL IN SHARK GILLNET AND ROCK LOBSTER FISHERIES............................................................................................................22 4 NEED................................................................................................................................30 5 OBJECTIVES ...................................................................................................................35 6 ASSESSMENT OF A SEA LION EXCLUSION DEVICE FOR MITIGATING BYCATCH IN THE SOUTHERN ROCK LOBSTER FISHERY ...............................................................36 INTRODUCTION ...................................................................................................................36 METHODS...........................................................................................................................37 Pup morphometric measurements ..............................................................................37 Sea lion rock lobster pot-exclusion trials.....................................................................37 Industry trials...............................................................................................................39 Data analysis...............................................................................................................39 Sea lion pot interaction trials................................................................................39 Industry trials .......................................................................................................40 RESULTS............................................................................................................................40 Southern rock lobster pot dimensions and spike height configurations ......................40 Pup morphometric measurements ..............................................................................41 Sea lion pot interaction trials .......................................................................................41 Industry trials...............................................................................................................43 DISCUSSION .......................................................................................................................44 7 ASSESSMENT AND IMPACT OF BYCATCH IN THE GILLNET SECTOR OF THE GHAT FISHERY ON AUSTRALIAN SEA LION SUBPOPULATIONS OFF SOUTH AUSTRALIA .....................................................................................................................59 INTRODUCTION ...................................................................................................................59 METHODS...........................................................................................................................60 Approach.....................................................................................................................60 Seal distribution and population size...........................................................................60 Distribution of sea lion foraging effort..........................................................................61 Spatial and temporal distribution of fishing effort ........................................................65 Modelling sea lion bycatch ..........................................................................................66 Estimating impacts of sea lion bycatch on subpopulations .........................................68 RESULTS............................................................................................................................71 Population distribution and abundance .......................................................................71 Models describing the distribution of ASL foraging effort............................................71 Distribution of fishing effort and catch, and overlap with ASL foraging effort..............73 Bycatch rates ..............................................................................................................75 Observed bycatch rates.......................................................................................75 Bycatch rate estimating method ..........................................................................75 Total ASL bycatch mortality in SA...............................................................................77 4 Table of contents Subpopulation bycatch mortality .................................................................................80 Impact of bycatch on subpopulations..........................................................................80 DISCUSSION .......................................................................................................................82