Report Commissioned by Inland Fisheries Ireland A preliminary assessment of the potential impacts of Cormorant Phalacrocorax carbo predation on salmonids in four selected river systems Citation for bibliographic purposes Tierney, N., Lusby, J., & Lauder, A. (2011) A preliminary assessment of the potential impacts of Cormorant Phalacrocorax carbo predation on salmonids in four selected river systems, a Report Commissioned by Inland Fisheries Ireland and funded by the Salmon Conservation Fund A preliminary assessment of the potential impacts of Cormorant Phalacrocorax carbo predation on salmonids in four selected river systems. Tierney, N., Lusby, J., & Lauder, A. (2011) TABLE OF CONTENTS Table of contents ........................................................................................................................................................................................1 List of tables..................................................................................................................................................................................................3 List of maps and figures...........................................................................................................................................................................3 List of photographs....................................................................................................................................................................................4 SUMMARY.....................................................................................................................................................................................................5 ACKNOWLEDGEMENTS.........................................................................................................................................................................8 1. INTRODUCTION..............................................................................................................................................................................9 1.1 Status and distribution.................................................................................................................................................................9 1.1.1 Great Britain ................................................................................................................................................................................... 11 1.2.2 Ireland............................................................................................................................................................................................... 12 1.2 Factors influencing the population expansion........................................................................................................... 18 1.2.1 Increased protection................................................................................................................................................................... 18 1.2.2 Increased stocking....................................................................................................................................................................... 19 1.2.3 Eutrophication............................................................................................................................................................................... 20 1.2.4 Disuse of toxins ............................................................................................................................................................................. 20 1.3 Diet........................................................................................................................................................................................................ 21 1.3.1 Methods for assessing diet....................................................................................................................................................... 21 1.3.2 Daily food intake........................................................................................................................................................................... 26 1.3.3 Diet in Europe................................................................................................................................................................................ 28 1.3.4 Diet in Ireland ................................................................................................................................................................................ 30 1.4 Salmon and Eel ecology and status..................................................................................................................................... 32 1.4.1 Atlantic Salmon ............................................................................................................................................................................. 32 1.4.2 European Eel .................................................................................................................................................................................. 36 1.5 Interactions with fisheries and mitigation .................................................................................................................... 38 1.5.1 Interactions with fisheries ....................................................................................................................................................... 38 1.5.2 Damage to individual fish ......................................................................................................................................................... 43 1.5.3 Mitigation......................................................................................................................................................................................... 43 1.6 Objectives......................................................................................................................................................................................... 49 2. CORMORANT SURVEY.............................................................................................................................................................. 51 1 A preliminary assessment of the potential impacts of Cormorant Phalacrocorax carbo predation on salmonids in four selected river systems. Tierney, N., Lusby, J., & Lauder, A. (2011) 2.1 Background...................................................................................................................................................................................... 51 2.2 Survey areas and Methods....................................................................................................................................................... 53 2.2.1 Survey areas ................................................................................................................................................................................... 53 2.2.2 Methods............................................................................................................................................................................................ 56 2.3 Results................................................................................................................................................................................................. 62 2.3.1 Survey effort................................................................................................................................................................................... 62 2.3.2 Weather............................................................................................................................................................................................ 63 2.3.3 Cormorant densities.................................................................................................................................................................... 63 2.3.4 Other Piscivores............................................................................................................................................................................ 76 3. DIRECT OBSERVATIONS OF FORAGING BIRDS......................................................................................................... 83 3.1 Background...................................................................................................................................................................................... 83 3.2 Methods.............................................................................................................................................................................................. 84 3.3 Results................................................................................................................................................................................................. 85 4. DIETARY ANALYSIS USING REGURGITATED SAMPLES...................................................................................... 86 4.1 Methods.............................................................................................................................................................................................. 86 4.1.2 Dietary sample collection methods.....................................................................................................................................