Spatial and Temporal Distribution of Harbour Porpoises in Relation to Their Prey
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S SPATIAL AND TEMPORAL DISTRIBUTION OF PA HARBOUR PORPOISES IN RELATION TO T IAL AN IAL thEIR PREY The population status of harbour porpoises has been of D concern for several years due to anthropogenic influ- T EMPORAL EMPORAL ences, especially incidental bycatch in gillnet fisheries. Proper management of a wide-ranging species such as the harbour porpoise requires reliable information on distribution, migrations, status of biological populations, and habitat preferences. This PhD thesis examines these D IS issues. Harbour porpoise distribution is examined by means T of satellite tracking (Paper II) and acoustic surveys, along RIBU with the agreement in results between these two very dif- ferent methods (Paper III). The data from satellite tracking T ION OF are also used to identify the boundaries of a genetically distinct harbour porpoise population and new abundance estimates are calculated for this population (Paper IV). Next, the underlying causes governing harbour porpoise H ARBOUR PORPOISES IN RELA IN PORPOISES ARBOUR distribution are explored by reviewing available informa- tion on harbour porpoise diet (Paper V) and correlating the distribution of satellite tracked porpoises with distribution of a main prey species, herring (Paper VI). Finally, the seaso- nal variations in distribution of harbour porpoises observed in a Danish strait, the Sound, are explored by examining the stomach content of porpoises from the area. Overall, this PhD thesis introduces several new applications for satellite telemetry data that – in combination with acoustic surveys – has significantly contributed to the current knowledge of harbour porpoise distribution. Furthermore, the thesis provides evidence of a porpoise-prey relationship which is important information in the conservation of the species, T due to its influence on harbour porpoise distribution. ION T O th EIR PREY EIR SPATIAL AND TEMPORAL DISTRIBUTION OF HARBOUR PORPOISES IN RELATION TO thEIR PREY PhD thesis 2011 Signe Sveegaard DANMARKS MILJØUNDERSØGELSER ISBN: 978-87-7073-000-0 AU AARHUS UNIVERSITET PAPER I Harbour porpoise distribution: Methods, ecology and movement in Danish and adjacent waters – a review Signe Sveegaard (her skal ikke stå noget om In prep. da det jo blot er en introduktion til resten af Phd’en) SPATIAL AND TEMPORAL DISTRIBUTION OF HARBOUR PORPOISES IN RELATION TO THEIR PREY PhD thesis 2011 Signe Sveegaard Data sheet Title: Spatial and temporal distribution of harbour porpoises in relation to their prey Subtitle: PhD thesis Author: Signe Sveegaard Affiliation: Dep. of Arctic Environment, National Environmental Research Institute, Aarhus University Publisher: National Environmental Research Institute (NERI) © Aarhus University, Denmark URL: http://www.neri.dk Year of publication: March 2011 Please cite as: Sveegaard, S. 2011: Spatial and temporal distribution of harbour porpoises in relation to their prey. PhD thesis. Dep. of Arctic Environment, NERI. National Environmental Research Institute, Aarhus University, Denmark. 128 pp. Abstract: The population status of harbour porpoises has been of concern for several years due to anthro- pogenic influences, especially incidental bycatch in gillnet fisheries. Proper management of a wide-ranging species such as the harbour porpoise requires reliable information on distribution, migrations, status of biological populations, and habitat preferences. This PhD thesis examines these issues. Harbour porpoise distribution is examined by means of satellite tracking (Paper II) and acoustic surveys, along with the agreement in results between these two very different methods (Paper III). The data from satellite tracking are also used to identify the boundaries of a genetically distinct harbour porpoise population and new abundance estimates are calculated for this population (Paper IV). Next, the underlying causes governing harbour porpoise distribu- tion are explored by reviewing available information on harbour porpoise diet (Paper V) and correlating the distribution of satellite tracked porpoises with distribution of a main prey species, herring (Paper VI). Finally, the seasonal variations in distribution of harbour porpoises observed in a Danish strait, the Sound, are explored by examining the stomach content of porpoises from the area. Overall, this PhD thesis introduces several new applications for satellite telemetry data that – in combination with acoustic surveys – has significantly contributed to the current knowl- edge of harbour porpoise distribution. Furthermore, the thesis provides evidence of a porpoise- prey relationship which is important information in the conservation of the species, due to its influence on harbour porpoise distribution. Keywords: Harbour porpoise, Phocoena phocoena, satellite tracking, acoustic surveys, distribution, prey, diet, herring, cod, Kattegat, Skagerrak, Belt Sea, the Sound PhD supervisors: Kim N. Mouritsen, Dept. of Marine Ecology, Biological Institute, Aarhus University and Jonas Teilmann, Dept. Arctic Environment, National Environmental Research Institute, Aarhus University PhD opponents: Dr. Andrew J. Read, Nicholas School of the Environment and Earth Sciences, Duke University, USA and Prof. Dr. ir. Peter J. H. Reijnders, Institute for Marine Ressources & Ecosystem Studies, The Netherlands. Layout and Drawings: NERI Graphics Group, Silkeborg Cover photo: (c) Bill Curtsinger, National Geographic Image Collection. Harbour porpoise in the Bay of Fundy, Canada. Photos inside PhD: Lars Laursen (www.uwphoto.dk), Andreas Nygren and Signe Sveegaard ISBN: 978-87-7073-222-2 Printed by: Rosendahls – Schultz Grafisk a/s Number of pages: 128 Circulation: 70 Internet version: The report is also available in electronic format (pdf) at NERI’s website http://www.dmu.dk/Pub/phd_sign.pdf Content PREFACE & ACKNOWLEDGEMENTS 5 DANSK RESUMÉ 6 ENGLISH SUMMARY 8 Paper I 11 Harbour porpoise distribution: Methods, ecology and movement in Danish and adjacent waters – a review Paper II 35 High-density areas for harbour porpoises (Phocoena phocoena) identified by satellite tracking Paper III 61 Acoustic surveys confirm high density areas of harbour porpoises found by satellite tracking Paper IV 73 Status of a harbour porpoise population - evidence of population separation and declining abundance Paper V 85 Prey availability and preferences of harbour porpoises in Kattegat and adjacent waters – a review Paper VI 101 Spatial aggregation of harbour porpoises determined by herring distribution Paper VII 115 Seasonal correlation identified between the distribution of harbour porpoises and their prey (c) Bill Curtsinger, National Geographic Image Collection PhD thesis by Signe Sveegaard PREFACE & ACKNOWLEDGEMENTS This thesis is the result of a three year PhD project, Several projects in this PhD have involved coop- conducted at the National Environmental Research eration with people at other institutes which also Institute (NERI), Aarhus University. deserves thanks. Roland Lick, Hilde Aarefjord, Carl Kinze, Patrik Börjesson, and Per Berggren are The work has concentrated on abundance and thanked for providing data for the prey analysis distribution of harbour porpoises, the validity of and for fruitful discussions on the best practice for methods used for studying this distribution and prey analysis. Douglas Gillespie, Andreas Nygren the underlying causes determining the movements andthe crew on RV Skagerak are is thanked for and distribution of porpoises. These topics are cur- scientific advice and help in the field during the rently of great scientific and political interest, due acoustic surveys. Furthermore, I thank all my part- to the implementation of the EC Habitat Directive ners at DTU Aqua for valuable and fruitful col- in Europe, scheduled to be concluded in 2012. laboration. The thesis consists of seven manuscripts of which During the lay-out phase of this PhD, I came into two are accepted for publication in peer reviewed contact with National Geographic photographer, journals (II & III), one has been submitted (VI), two Bill Curtsinger, and underwater photographer, are nearly ready for submission (IV & VII), one Lars Laursen, who kindly donated their amazing awaits further data in order to be completed (V) photos to be used in this thesis. Thank you. and the last manuscript (I) represents an introduc- tion to the thesis in form of a review paper. I wish to thank my family and friends for their support and encouragement throughout this This thesis was supervised by Jonas Teilmann study. And, finally, I owe my deepest thanks to and Kim N. Mouritsen and I owe them both great Morten for all the help and support you have given thanks. Jonas; from I met you in 2004 you have throughout this PhD and for being so incredibly impressed me with your knowledge, capability of cool about my many hours away from home du- handling stressful situations and your good hu- ring field work and conferences. mour. Thank you for believing in me, for includ- ing me in your work and for all your help through- This PhD was funded in cooperation between the out this PhD. Kim; your statistical skills, ecological NERI, Aarhus University, Roskilde and the Faculty knowledge and cool Jutlandic mind has made a of Science, Aarhus University, Aarhus. great contribution to this PhD. I thank both my supervisors for always taking the time to discuss different projects with me, in spite of your busy schedules. Numerous other people have contributed to this PhD. I wish to thank all my colleagues at the De- partment of Arctic Environment