What is causing the decline of little penguins (Eudyptula minor) on Granite Island, South Australia? Report to the South Australian Department for Environment and Heritage, Wildlife Conservation Fund and the Nature Foundation SA Natalie M Bool1, Brad Page2 and Simon D Goldsworthy2 1 University of Adelaide, North Terrace Adelaide SA 5009 2 South Australian Research and Development Institute (SARDI), 2 Hamra Avenue, West Beach SA 5024 What is causing the decline of little penguins (Eudyptula minor) on Granite Island, South Australia? South Australian Research and Development Institute SARDI Aquatic Sciences 2 Hamra Avenue West Beach SA 5024 Telephone: (08) 8207 5400 Facsimile: (08) 8207 5481 http://www.sardi.sa.gov.au/ Disclaimer Copyright South Australian Research and Development Institute 2007. 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, July 2007 SARDI Aquatic Sciences Publication Number F2007/000288-1 SARDI Research Report Series No. 217 Authors: Bool NM, Page B, and Goldsworthy SD Reviewers: Dr Shane Roberts and Dr Adrian Linnane Approved by: Dr. T. Ward Signed: Date: 12 July 2007 Circulation: Public Domain 2 Table of Contents 1 Executive Summary ................................................................................................. 5 2 Background.............................................................................................................. 6 3 Introduction .............................................................................................................. 8 Aims and approach of the project ..........................................................................11 4 Methods ................................................................................................................. 12 Burrow monitoring ..............................................................................................12 Date of laying and fledging.................................................................................13 Analysis of reproductive success .......................................................................13 Chick growth rate ...............................................................................................13 Census of the breeding population.....................................................................14 Historical data.....................................................................................................14 Foraging ecology....................................................................................................15 Data analyses.....................................................................................................15 Spatial overlap in foraging area..........................................................................16 Little penguin diet ...............................................................................................17 Diet of New Zealand fur seals ................................................................................18 5 Results ................................................................................................................... 21 Reproductive success ............................................................................................21 Predation by rats ................................................................................................21 Inter-annual breeding success at Granite Island................................................21 Inter-annual breeding success at West Island ...................................................21 Chick growth.......................................................................................................22 Population census during the breeding season .................................................23 Foraging ecology................................................................................................24 Summary of foraging behaviour .........................................................................25 Foraging parameters..........................................................................................25 Oceanography....................................................................................................27 Overlap of foraging areas between Granite and West Island penguins.............29 Penguin Diet...........................................................................................................29 Size and weight of prey......................................................................................31 Comparison of diet between colonies ................................................................31 New Zealand fur seal diet...................................................................................32 Number of New Zealand fur seals hauled-out....................................................33 6 Discussion.............................................................................................................. 34 Reproductive parameters.......................................................................................34 Impacts of tourism and predation by rats on little penguins ...................................36 Predation by New Zealand fur seals ......................................................................37 Foraging parameters..............................................................................................38 Similarity in prey diversity and meal sizes..............................................................40 Chick growth rates .................................................................................................41 The future of the little penguin populations at Granite and West Islands...............42 7 Conclusions............................................................................................................ 45 8 Recommendations for future research................................................................... 47 9 References............................................................................................................. 48 10 Acknowledgements .............................................................................................. 55 3 List of Figures Figure 1. The location of Granite and West Islands and other islands mentioned in the text. ...............................................................................7 Figure 2. The number of active little penguin burrows during the breeding season reported at Granite Island from 2001-2006. ...............................24 Figure 3. Circular histogram of the mean direction of travel of breeding little penguins from Granite (blue) and West Islands (red) in 2006.................25 Figure 4. Summary of the inferred foraging routes undertaken by little penguins at Granite Island (red) and West Island (blue) based on satellite tracking in 2006. .....................................................................................26 Figure 5. The proportional time spent foraging in oceanic areas of 1 x 1 km grids by 10 little penguins from Granite Island. Proportional time spent in each grid is indicated by colour: where red represents regions where penguins spent more time followed by orange, yellow, green and finally blue areas where penguins spent relatively little time.............................26 Figure 6. The proportional time spent foraging in oceanic areas of 1 x 1 km grids by 8 little penguins at West Island. Proportional time spent in each grid is indicated by colour: where red represents regions where penguins spent more time followed by orange, yellow, green and finally blue areas where penguins spent relatively little time...............................................27 Figure 7. The average number of New Zealand fur seals hauled-out at Seal Rocks, West Island and Granite Island between March-October 2006...33 List of Tables Table 1. Measures of reproductive success for Granite and West Islands from 1990 – 2006. Data from 1990 - 2005 were obtained from the Granite Island Little Penguin Monitoring Group (N. Gilbert and R. Brandle unpubl. data). ......................................................................................................22 Table 2. Growth parameters of 12 little penguin chicks at Granite Island in 2006........................................................................................................23 Table 3. Growth parameters of 11 little penguin chicks at West Island in 2006. ................................................................................................................23 Table 4. Summary of the foraging parameters of little penguins at Granite and West Islands in 2006. .............................................................................28 Table 5. Summary data of the oceanographic characteristics of the areas that the little penguins foraged in from Granite and West Islands in 2006. ....29 Table 6. The prey consumed and their relative numerical abundance (NA) and frequency of occurrence (FO) in stomach contents of little penguins from the Granite and West Island colonies in 2006. The number of samples examined, the number with prey remains and the minimum number of individuals consumed were 37, 37 and 191 respectively. ......30 Table