Genetic variation and population structure: using the mtDNA hypervariable control region to study the eastern and western stocks of Steller sea lions (Eumetopias jubatus)

Megan Lambert, Robert Trujillo, Dr. Thomas Loughlin*,

Dr. Thomas Gelatt**, and Dr. John Bickham

 The Steller sea lion (Eumetopias jubatus) is a marine mammal that has experienced a drastic population decline since the 1970’s.  Previous studies have shown the population to be composed of three genetically differentiated populations: an eastern stock that occurs east of 144W to Northern California, a western stock that occurs west of 144W to the Commander Islands, Russia, and an Asian stock that includes rookeries in the Kuril Islands, Sea of Okhotsk, and the Kamchatka Peninsula.  Migration among stocks is highly constrained, but low levels have been observed from the western stock into thewestern-most rookeries of the eastern stock in southeastern Alaska.  This study examines a larger sample size than previously available taken from both eastern and western stock rookeries.  Flipper punch samples were obtained from approximately 400 animals in southeastern Alaskan rookeries during fieldwork this summer.  The purpose of this study is to examine introgression between the western stock and the eastern stock by examining increased samples sizes from eastern stock rookeries in California (n = 51) and Oregon (n = 84) and from western stock rookeries in Alaska.  The haplotype of each sea lion is determined by comparing the sequence to existing data obtained over the past ten years from > 1,700 Steller sea lions from throughout the range.  Five instances of ostensible dispersal events have been found at Rogue Reef and two at St. George Reef.  The primary direction of introgression is from the western stock into the eastern stock.

* National Marine Mammal Laboratory, National Marine Fisheries Service,

** Alaska Department of Fish and Game, Division of Wildlife Conservation

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