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Downloaded from orbit.dtu.dk on: Dec 18, 2017 The importance of habitat structure for the distribution and behaviour of demersal fish Kristensen, Louise Dahl; Støttrup, Josianne Gatt; Stenberg, Claus; Grønkjær, P. Publication date: 2016 Document Version Publisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Kristensen, L. D., Støttrup, J. G., Stenberg, C., & Grønkjær, P. (2016). The importance of habitat structure for the distribution and behaviour of demersal fish. Technical University of Denmark. National Institute of Aquatic Resources. 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The importance of habitat structure for the distribution and behaviour of demersal fi sh PhD Thesis PhD Thesis Written by Louise Dahl Kristensen Defended 18 may 2016 The importance of habitat structure for the distribution and behaviour of demersal fish Louise Dahl Kristensen PhD Thesis 2016 Technical University of Denmark National Institute of Aquatic Resources Section for Ecosystem based Marine Management PhD thesis Louise Dahl Kristensen Main supervisor: Josianne Gatt Støttrup, Senior Research Scientist, DTU Aqua Co supervisor: Claus Stenberg, Senior Statistical Programmer, Novo Nordisk Co supervisor: Peter Grønkjær, Associate Professor, Aarhus University Front page illustration by Søren Kristensen 2 PhD thesis Louise Dahl Kristensen TABLE OF CONTENTS PREFACE .......................................................................................................................................... 5 ENGLISH SUMMARY ..................................................................................................................... 6 DANSK RESUMÉ ............................................................................................................................. 7 LIST OF PAPERS ............................................................................................................................. 8 INTRODUCTION ............................................................................................................................. 9 Background ......................................................................................................................................................9 Aim and objective ....................................................................................................................................... 14 Outline ............................................................................................................................................................. 15 THE IMPORTANCE OF HABITAT STRUCTURE FOR FISH ............................................... 16 Effect of habitat structure on biodiversity and abundance .................................................... 16 Effect of habitat structure on growth and animal body-size .................................................. 19 Effect of habitat structure on predator-prey interactions ....................................................... 21 EVALUATION OF THE METHODOLOGY................................................................................ 23 Biogenic reef (Paper I) ............................................................................................................................. 23 Boulder reef (Paper II, III, IV) ............................................................................................................... 25 Perspectives for establishment or restoration of habitat structures ................................. 26 CONCLUSIONS .............................................................................................................................. 27 Biogenic reef (Paper I) ............................................................................................................................. 27 Boulder reef (Paper II, III, IV) ............................................................................................................... 27 Establishment or restoration of habitat structures .................................................................... 28 REFERENCES ................................................................................................................................. 29 PAPER I ........................................................................................................................................... 37 PAPER II ......................................................................................................................................... 55 PAPER III ........................................................................................................................................ 73 PAPER IV ........................................................................................................................................ 93 3 PhD thesis Louise Dahl Kristensen 4 PhD thesis Louise Dahl Kristensen PREFACE This thesis is the result of a three year PhD project at the Technical University of Denmark at the National Institute of Aquatic Resources. The PhD has been completed alongside a part time position as administrative assistant for the Key Fishermen project where volunteer recreational fishermen contributed to the project with their catches from gill nets and fyke nets from fixed locations all over Denmark. In addition, the PhD has been prolonged due to two family additions, the writing of a report on the Key Fishermen project and editing of a report on the effect of stone reefs as nursery and spawning area. The PhD was carried out at the National Institute of Aquatic Resources, Technical University of Denmark (DTU Aqua) in collaboration with Department of Bioscience - Aquatic Biology at Aarhus University. The research was financed by the European Fishery Fund and the Danish Marine Coastal Fisheries Management Program (Fiskepleje). Many people are to be thanked for their support and involvement in my PhD project. My greatest gratitude goes to Josianne Støttrup for pushing me to achieve my best and for believing in me from the very beginning. I have learned much from you, and I thank you for the past nine years of our professional collaboration. I am grateful to Claus Stenberg for his advice and encouragement throughout my PhD. I enjoyed the many hours we spent together at sea collecting data. In spite of the long days you were always able to lift the spirit of the crew. And thank you, for always being available for statistical help. I would like to thank Peter Grønkjær for his help and trust in me. You were the familiar face in the tentative beginning of this project and that means more than I can say. I would also like to thank all the people at DTU Aqua. Stine Kærulf Andersen, Louise K. Poulsen, Helle Torp Christensen and Jesper Knudsen, it was a pleasure working with you and I learned a lot from you all. Thanks also to my office mates Eleonora, Filipa and Elliot, I enjoyed the time we shared in our office. Viola, I hate to finish without you, hurry up! I had not been able to collect my data without volunteering fisherman, Poul Erik Nielsen – I am very thankful for your endurance. My warmest thanks go to my family and friends, who continuously encouraged and supported me throughout the PhD. You have all been a tremendous help to me. My warmest thanks go to Signe for her support and love through the ups and downs of the PhD – you are my rock! And to my children Laura & Lauritz for always putting things in perspective, making me forget hard times and enjoy the moment. Louise Dahl Kristensen Sydhavnen, 1st of April 2016 5 PhD thesis Louise Dahl Kristensen ENGLISH SUMMARY This PhD project investigated the effects of coastal habitat structural characteristics on the biodiversity, abundance, size range and behaviour of fish, whilst maintaining a particular focus on the effect of habitat restoration. Fish distribution and behaviour was measured using a combination of gill net sampling, video recordings and acoustic telemetry. Some biogenic temperate reefs have declined to commercial extinction, in several countries, due to a host of impacts, including overexploitation, parasites and the loss of hard biogenic substrate. The recovery of these reefs may be slow or, without sufficient hard bottom, even impossible. Bivalves are ecosystem engineers as they modify the benthic environment and influence the health of other organisms. Additionally, biogenic reefs provide ecosystem services such as reducing turbidity and improving water quality which make bivalves ideal organisms for consideration in habitat restoration project. In the present thesis, blue mussel (Mytilus edulis) beds were established cost- effectively using crowdsourcing and the help of local volunteer fishermen (Paper I). A total of 44 tons of blue mussels were produced and established in beds over an area