Patterns of Distribution, Abundance, and Change over Time in the Marine Bird Community of PDF
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AN ABSTRACT OF THE THESIS OF Daniel A. Cushing for the degree of Master of Science in Wildlife Science presented on June 10, 2014. Title: Patterns of Distribution, Abundance, and Change over Time in the Marine Bird Community of Prince William Sound, Alaska, 1989-2012. Abstract approved: ___________ __________________________________________ Daniel D. Roby Over recent decades, the marine ecosystems of Prince William Sound (PWS), Alaska have experienced the concurrent effects of a major anthropogenic disturbance, the 1989 Exxon Valdez oil spill (EVOS), and a dynamic atmospheric-oceanic environment. Studies of top marine consumers can provide insights into processes of ecosystem change. Using data collected during boat-based marine bird surveys in PWS over the period 1989-2012, I used complimentary taxon- and community-centric approaches to investigate patterns of distribution and abundance of marine birds across space and time. In doing so, I sought to provide insight into processes that may have affected both the birds themselves and the ecosystems of which they are a part. I found that the marine bird community as a whole was spatially structured along a primary onshore-offshore environmental gradient, and secondarily structured along an estuarine-marine environmental gradient. I found two patterns of community variability across time. The first temporal community-level pattern was likely related to sustained rates of change in the abundance of some genera, likely caused by demographic processes. This pattern was correlated with climate variability at time-scales of several years to a decade. The second temporal community-level pattern was characterized by fluctuations that correlated with climate variability at an annual time-scale, likely caused by movements of birds between PWS and the adjacent Gulf of Alaska. I also evaluated changes in the abundance of 18 genera of marine birds, and found that seven had declined in abundance and three had increased over the study period; all genera that declined were piscivorous or planktivorous. Furthermore, the rates of population change of genera were related to their position in the onshore-offshore gradient, with the highest rates of decline occurring in offshore-associated genera. I also investigated spatial habitat associations and temporal changes in abundance of a focal taxon, the seabird genus Brachyramphus. Two species within this piscivorous, pursuit-diving genus occur in PWS, the marbled murrelet (B. marmoratus) and the Kittlitz’s murrelet (B. brevirostris). Both are species of conservation concern, and both experienced acute mortality in PWS caused by the EVOS. Using a statistical model that accounted for variables affecting observed abundance across space and time, I found that abundance decreased by more than two-thirds over the study period. I found no evidence that rates of change differed along environmental or geographic gradients. There was also no evidence that changes in seasonal patterns of abundance occurred. These results are indicative of a widespread decline in the abundance of Brachyramphus murrelets within PWS. Taken as a whole, the results of my thesis are consistent with the hypothesis that climate change has differentially affected nearshore and offshore components of PWS food webs. This in turn has likely contributed to the failure of some taxa, including Brachyramphus murrelets, to recover from population injury caused by the EVOS. © Copyright by Daniel A. Cushing June 10, 2014 All Rights Reserved Patterns of Distribution, Abundance, and Change over Time in the Marine Bird Community of Prince William Sound, Alaska, 1989-2012 by Daniel A. Cushing A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Presented June 10, 2014 Commencement June 2015 Master of Science thesis of Daniel A. Cushing presented on June 10, 2014. APPROVED: Major Professor, representing Wildlife Science Head of the Department of Fisheries and Wildlife Dean of the Graduate School I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. Daniel A. Cushing, Author ACKNOWLEDGMENTS I am grateful to numerous people who have contributed to this study and to my graduate education. This long-term study was carried out by many people over a period of decades, and I am indebted to all of them. Dr. Steve Klosiewski and Doug Burns designed and carried out a robust marine bird survey program in the immediate aftermath of a major oil spill. This long-term study also depended on the hard work and persistence of many principal investigators and project leaders over the years, including Dr. Beverly Agler, Julian Fisher, Dr. David Irons, Steve Kendall, Dr. Kathy Kuletz, Karen Laing, Brian Lance, Aly McKnight, Shawn Stephensen, and Kelsey Sullivan. I especially thank Aly McKnight and Kelsey Sullivan for generously sharing their knowledge and advice. Many observers participated in this study, and I thank all of them, particularly the capable, dedicated, and good-spirited members of the 2010 and 2012 winter and summer survey teams: Lisa Andreano, Eric Baker, Andy Bankert, Emily Bernhardt, Karen Brenneman, Niels Dau, Chris Ford, Robb Kaler, Liz Labunski, Jeremy O'Donnell, Adam Peck-Richardson, Marty Reedy, Tanya Sandberg-Diment, Ana Santos, Patty Sullivan, Mike Walgren, Gloria Zager, and Tamara Zeller. Karen Brenneman was instrumental in making the surveys safe, successful, and fun. Thanks also to all those who provided us with shelter and support along the way. I am grateful to David Reggiani of Prince William Sound Aquaculture Corporation and to the staff of the Armin F. Koernig Hatchery for their generosity and hospitality, and also to David and Annette Janka of the vessel Auklet and David Beam and Cedar Stark of the vessel Montague for their exceptional service. I am deeply grateful to my advisor, Dr. Daniel Roby, for his mentorship and support throughout my graduate education, and for his insight. I am also deeply grateful to Dr. David Irons for providing me with outstanding opportunities for learning and growth, and for contributing his ideas and expertise. I thank Dr. Bruce McCune, a member of my graduate advisory committee, for his many thoughtful contributions, and also my Graduate Council Representative, Dr. Howard Gelberg, for his involvement. I also thank Dr. Jim Peterson and Dr. John Van Sickle for their statistical advice and Dr. Don Lyons for his invaluable guidance. In addition, Dr. Daniel Vernon was instrumental in shaping my interest in a research career, and S. Kim Nelson helped form my research interest in the ecology of marine birds. The Prince William Sound survey program was funded by the Exxon Valdez Oil Spill Trustee Council and by the U.S. Fish and Wildlife Service. My graduate work was primarily funded by the U.S. Fish and Wildlife Service. I was also supported by a Graduate Student Research Award from the North Pacific Research Board. In addition, I received support from the Oregon State University Graduate School, College of Agricultural Sciences, and Department of Fisheries and Wildlife, as well as the Gamma Sigma Delta Honor Society. I am extraordinarily grateful for this support. I am also thankful for my many friends, classmates, office-mates, and colleagues here in Corvallis, who provided much-needed friendship, inspiration, and distraction. Special thanks to my lab-mates Jessica Adkins, Lindsay Adrian, Kirsten Bixler, Stefanie Collar, Nick Hatch, Tim Lawes, James Lawonn, Pete Loschl, Tim Marcella, Allison Patterson, Adam Peck-Richardson, Dr. Yasuko Suzuki, and James Tennyson for their ideas, assistance, and advice. And last of all, I thank my family, and especially my wonderful wife, Amanda Cushing, for her boundless patience, love, and support. CONTRIBUTION OF AUTHORS Dr. Daniel Roby helped to shape the objectives of this thesis and provided editorial review of all chapters. Dr. David Irons secured project funding, managed the long-term seabird survey program upon which this thesis is based, and provided editorial comments. Dr. Kathy Kuletz secured project funding, supported fieldwork, and contributed editorial comments. TABLE OF CONTENTS Page CHAPTER 1: GENERAL INTRODUCTION ................................................................ 1 LITERATURE CITED ............................................................................................... 6 CHAPTER 2: TEMPORAL CHANGE IN A SUBARCTIC MARINE BIRD COMMUNITY LINKED TO HABITAT AND CLIMATE CHANGE ................................ 9 ABSTRACT ............................................................................................................ 10 INTRODUCTION ................................................................................................... 11 METHODS ............................................................................................................. 15 Study area .......................................................................................................... 15 Modes of atmospheric-oceanic variability ........................................................... 19 Spatial structure of the marine bird community .................................................. 20 Relationships between spatial community structure and habitat ........................ 22 Rates of change in abundance of genera ........................................................... 22 Temporal structure of the marine bird community .............................................. 23 Relationships between temporal community structure and atmospheric-oceanic variability ............................................................................................................. 24 Relationships between temporal changes and spatial community structure ...... 25 RESULTS .............................................................................................................. 25 Spatial structure of the marine bird community .................................................. 25 Relationships between spatial community structure and habitat ........................ 26 Rates of change in abundance of genera ........................................................... 27 Temporal structure of the marine bird community .............................................. 27 Relationships between temporal structure of the marine bird community and atmospheric-oceanic variability ........................................................................... 29 Relationships between temporal changes and spatial structure of the marine bird community .......................................................................................................... 30 DISCUSSION......................................................................................................... 32 Spatial structure of the marine bird community and relationships between community structure and habitat ......................................................................... 32 Changes in abundance and community composition over time, and relationships between temporal changes and atmospheric-oceanic variability ....................... 34 Relationships between temporal changes and the spatial structure of the marine bird community ................................................................................................... 36 Conservation implications ................................................................................... 36 LITERATURE CITED ............................................................................................. 39
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