RESOURCE COMPETITION, SPACE USE AND FORAGE ECOLOGY OF SEA OTTERS, ENHYDRA LUTR1S, IN SOUTHERN SOUTHEAST ALASKA By Zachary Hoyt RECOMMENDED: Dr. M. Tim Tinker Dr. Franz Mueter Dr. Chr/s Siddon S'* Dr. Ginny Eek Advisory Committee Chair _±u Dr. Franz Mueter Chair, Graduate Program in Fisheries APPROVED: ( & l u ^ ( W AMOK- RESOURCE COMPETITION, SPACE USE AND FORAGE ECOLOGY OF SEA OTTERS, ENHYDRA LUTRIS, IN SOUTHERN SOUTHEAST ALASKA A DISSERTATION Presented to the Faculty of the University of Alaska Fairbanks in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY By Zachary Hoyt, B.S., M.S. Fairbanks, AK December 2015 Abstract The growing sea otter population in southern Southeast Alaska is impacting commercial shellfish, through foraging and expanding in range and abundance except where hunted for subsistence. Sea otters and their prey have coexisted in the North Pacific Ocean for approximately 750,000 years, but due to exploitation of sea otters from the 1770s until 1911, the species became extinct over much of its range, including southern Southeast Alaska. Subsequently, invertebrate species flourished and were commercially targeted in the late 1900s. Sea otters were relocated (n = 106) to southern Southeast Alaska in 1968. In this dissertation, I evaluated this marine mammal-fisheries conflict through multiple approaches. In Chapter 1, I analyzed geoduck clam and red sea urchin abundance surveys (1994-2012) and catch and effort data from commercial Dungeness crab fisheries (1969-2010) to identify interactions between sea otters and commercial shellfish. In Chapter 2, I collected geo-locations from 30 instrumented sea otters (2011-2014) to identify space use and range expansion. In Chapter 3, I collected sea otter abundance and distribution data from fixed wing aircraft (2010-2014) and observational forage data from sea otters (2010-2013) to determine contemporary population growth and consumption of commercially important shellfish by sea otters. The sea otter population in southern Southeast Alaska has grown from 106 to an estimated 13,139 individuals between 1968 and 2011 with an annual growth rate of 12% and expansion of its range by 117 km y- . 2Results 1 from a before- after, control-impact analysis indicate that sea otters are rapidly impacting red sea urchin and significantly reducing geoduck clam densities. Further, breakpoints predicted from regression models of Dungeness crab catch are correlated with known sea otter colonization timing. Forty- six percent of the population level diet of sea otters represented commercially important prey. Sea otters targeted commercially important species, specifically red sea urchins and Dungeness v crab, when first colonizing an area, after which the diet of sea otters became more diverse as colonization durations increased. Using habitat models based on a bivariate normal probability distribution function, environmental covariates and subsistence hunting pressure on sea otters, I determined that sea otter range expansion was limited by subsistence hunting. Further, female and non-territorial males segregated based on habitat and likely prey preferences. I conclude that sea otter populations will likely continue to grow, and that current shellfisheries cannot coexist with sea otters under existing management. Further, conservation and management of sea otter populations, whether to increase the distribution through translocation efforts or reduce the distribution to avoid human conflicts, could benefit from insights gained from spatially explicit modeling at the landscape level. vi Table of Contents Page Signature Page ........................................................................................................................................i Title Page ..............................................................................................................................................iii Abstract ................................................................................................................................................. v Table of Contents ................................................................................................................................ vii List of Figures .......................................................................................................................................xi List of Tables ..................................................................................................................................... xiii List of Appendices ............................................................................................................................. xiv Dedication and Acknowledgments ....................................................................................................xv General Introduction ..............................................................................................................................1 Sea otter biology and ecology ...........................................................................................................1 Sea otter history and demographics in Southeast Alaska .............................................................. 3 Purpose and organization of dissertation .........................................................................................7 Literature cited ................................................................................................................................. 9 Chapter 1: Reductions in commercially important macroinvertebrates associated with sea otters (Enhydra lutris) in Southeast Alaska ................................................................................................. 15 Abstract ........................................................................................................................................... 15 Introduction ..................................................................................................................................... 16 vii Methods ........................................................................................................................................... 21 Study area and species ................................................................................................................21 Red sea urchins ........................................................................................................................... 22 Geoduck clams ............................................................................................................................ 24 Dungeness crab ........................................................................................................................... 26 Results.............................................................................................................................................. 28 Red sea urchins ........................................................................................................................... 28 Geoduck clams ............................................................................................................................ 29 Dungeness crab ........................................................................................................................... 30 Discussion ....................................................................................................................................... 32 Acknowledgments ......................................................................................................................... 38 Literature cited ............................................................................................................................... 38 Tables .............................................................................................................................................. 48 Figures ............................................................................................................................................ 54 Chapter 2: Space use of northern sea otters (Enhydra lutris kenyoni) within an exploited and growing population..............................................................................................................................63 Abstract ........................................................................................................................................... 63 Keywords .........................................................................................................................................64 Introduction ......................................................................................................................................65 viii Methods ........................................................................................................................................... 68 Sexual segregation ...................................................................................................................... 73 Hunting ........................................................................................................................................73 Range expansion ......................................................................................................................... 74 Results.............................................................................................................................................. 74 Sexual segregation .....................................................................................................................