MMMaaarrriiinnneee EEEnnnvvviiirrrooonnnmmmeeennnttt &&& EEEcccooolllooogggyyy An Update of the Report: Understanding the Impediments to the Growth of Australian Sea Lion Populations Photo: S Goldsworthy (SARDI) Report to the Department of the Environment, Water, Heritage and the Arts SARDI Publication Number F2008/00847-1 SARDI Research Report series No. 356 SD Goldsworthy, J McKenzie, PD Shaughnessy, RR McIntosh, B Page, R Campbell An Update of the Report: Understanding the Impediments to the Growth of Australian Sea Lion Populations SD Goldsworthy1, J McKenzie1, PD Shaughnessy2, RR McIntosh3, B Page1, R Campbell4 1 South Australian Research & Development Institute (SARDI), 2 Hamra Avenue, West Beach SA 5024 2 South Australian Museum, North Terrace, Adelaide, SA 5000 3 Zoology Department, La Trobe University, Melbourne, Vic 3086 4 Western Australian Fisheries and Marine Research Laboratories, Department of Fisheries, PO Box 20, North Beach, Western Australia, 6920 South Australian Research and Development Institute SARDI Aquatic Sciences 2 Hamra Avenue West Beach SA 5024 Telephone: (08) 8207 5400 Facsimile: (08) 8207 5481 www.sardi.sa.gov.au Disclaimer Copyright Department of the Environment, Water, Heritage and the Arts, and South Australian Research and Development Institute 2009. This work is copyright. Except as permitted under the Copyright Act 1968 (Commonwealth), no part of this publication may be reproduced by any process, electronic or otherwise, without the specific written permission of the copyright owners. Neither may information be stored electronically in any form whatsoever without such permission. Printed in Adelaide, May 2009 SARDI Publication Number F2008/000847-1 SARDI Research Report Series No. 356 Authors: SD Goldsworthy, J McKenzie, PD Shaughnessy, RR McIntosh, B Page, R Campbell Reviewers: T Ward and K Wiltshire Approved by: J. Tanner Signed: Date: 1 May 2009 Circulation: Public Domain CONTENTS 1 EXECUTIVE SUMMARY ...................................................................1 2 INTRODUCTION................................................................................3 2.1 BACKGROUND.......................................................................................................................................................... 3 2.2 AIMS & OBJECTIVES OF DOCUMENT .................................................................................................................... 6 2.3 FORMAT OF THE REPORT ...................................................................................................................................... 6 3 DISTRIBUTION, ABUNDANCE AND POPULATION TRENDS .......7 3.1 DISTRIBUTION AND ABUNDANCE.......................................................................................................................... 7 3.1.1 Distribution ....................................................................................................................................................... 7 3.1.2 Historic context to current range and abundance ............................................................................................ 7 3.1.3 Estimates of pup abundance............................................................................................................................ 8 3.1.4 Population estimates...................................................................................................................................... 10 3.1.5 Population structure and subdivision ............................................................................................................. 10 3.2 TRENDS IN ABUNDANCE AT INDIVIDUAL COLONIES ........................................................................................ 16 3.2.1 Seal Bay......................................................................................................................................................... 16 3.2.2 The Pages Islands ......................................................................................................................................... 20 3.2.3 Seal Slide, Kangaroo Island........................................................................................................................... 22 3.2.4 Dangerous Reef............................................................................................................................................. 23 3.2.5 Jones Island................................................................................................................................................... 24 3.2.6 Olive Island .................................................................................................................................................... 25 3.2.7 Buller, North Fisherman and Beagle Islands.................................................................................................. 25 3.3 DISCUSSION ........................................................................................................................................................... 25 3.3.1 Data quality .................................................................................................................................................... 25 3.3.2 Poor quality time-series data on population trends........................................................................................ 26 3.3.3 Recent developments involving marked animals........................................................................................... 27 3.4 KNOWLEDGE GAPS ............................................................................................................................................... 27 4 NATURAL FACTORS AFFECTING POPULATION GROWTH ......28 4.1 REPRODUCTIVE BIOLOGY.................................................................................................................................... 28 4.1.1 Gestation........................................................................................................................................................ 28 4.1.2 Lactation ........................................................................................................................................................ 29 4.1.3 Breeding cycle................................................................................................................................................ 29 4.1.4 Evolutionary determinants of Australian sea lion life-history.......................................................................... 32 4.1.5 Knowledge gaps and further research ........................................................................................................... 34 4.2 POPULATION DEMOGRAPHY ............................................................................................................................... 34 4.2.1 Sexual maturity and longevity ........................................................................................................................ 34 4.2.2 Growth in body size........................................................................................................................................ 36 4.2.3 Reproductive rates......................................................................................................................................... 37 4.2.4 Survival and Mortality..................................................................................................................................... 40 4.2.5 Demographic models and Population Viability Analyses ............................................................................... 45 4.2.6 Detecting demographic change ..................................................................................................................... 52 4.2.7 Knowledge gaps and further research ........................................................................................................... 53 4.3 DISPERSAL ............................................................................................................................................................. 53 4.3.1 Knowledge gaps and further research ........................................................................................................... 54 4.4 CRITICAL HABITAT AND PREY AVAILABILITY..................................................................................................... 54 4.4.1 Terrestrial habitats ......................................................................................................................................... 54 4.4.2 Foraging habitats ........................................................................................................................................... 55 4.4.3 Prey availability .............................................................................................................................................. 69 4.4.4 Knowledge gaps and further research ........................................................................................................... 71 4.5 INTERSPECIFIC COMPETITION FOR FOOD RESOURCES................................................................................. 72 4.5.1 New Zealand fur seals ................................................................................................................................... 73 4.5.2 Australian Fur seals ......................................................................................................................................