Inter-population movements of steller sea lions in Alaska with implications for population separation

Lauri A Jemison; Grey W Pendleton; Lowell W Fritz; Kelly K Hastings; John M Maniscalco; Andrew W Trites; Tom S Gelatt

doi:10.1371/journal.pone.0070167

Inter-population movements of steller sea lions in Alaska with implications for population separation

PLoS One. 2013 Aug 5;8(8):e70167. doi: 10.1371/journal.pone.0070167. Print 2013.

Authors

Lauri A Jemison¹, Grey W Pendleton, Lowell W Fritz, Kelly K Hastings, John M Maniscalco, Andrew W Trites, Tom S Gelatt

Affiliation

¹ Division of Wildlife Conservation, Alaska Department of Fish and Game, Douglas, Alaska, USA. lauri.jemison@alaska.gov

Abstract

Genetic studies and differing population trends support the separation of Steller sea lions (Eumetopias jubatus) into a western distinct population segment (WDPS) and an eastern DPS (EDPS) with the dividing line between populations at 144° W. Despite little exchange for thousands of years, the gap between the breeding ranges narrowed during the past 15-30 years with the formation of new rookeries near the DPS boundary. We analyzed >22,000 sightings of 4,172 sea lions branded as pups in each DPS from 2000-2010 to estimate probabilities of a sea lion born in one DPS being seen within the range of the other DPS (either 'West' or 'East'). Males from both populations regularly traveled across the DPS boundary; probabilities were highest at ages 2-5 and for males born in Prince William Sound and southern Southeast Alaska. The probability of WDPS females being in the East at age 5 was 0.067 but 0 for EDPS females which rarely traveled to the West. Prince William Sound-born females had high probabilities of being in the East during breeding and non-breeding seasons. We present strong evidence that WDPS females have permanently emigrated to the East, reproducing at two 'mixing zone' rookeries. We documented breeding bulls that traveled >6,500 km round trip from their natal rookery in southern Alaska to the northern Bering Sea and central Aleutian Islands and back within one year. WDPS animals began moving East in the 1990s, following steep population declines in the central Gulf of Alaska. Results of our study, and others documenting high survival and rapid population growth in northern Southeast Alaska suggest that conditions in this mixing zone region have been optimal for sea lions. It is unclear whether eastward movement across the DPS boundary is due to less-optimal conditions in the West or a reflection of favorable conditions in the East.

Publication types

Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Adult
Alaska
Animals
Female
Humans
Male
Population Dynamics
Sea Lions / physiology*
Young Adult

Grants and funding

Funding for this study was provided to the Alaska Department of Fish and Game by the National Oceanic and Atmospheric Administration (NOAA) Fisheries Alaska Region under several grants from 2001–2012 (including NA11NMF4390200, NA08NMF4390544, NA04NMF4390170, NA17FX1079) and by the Outer Continental Shelf Oil and Gas Revenues, Coastal Impact Assistance Program, United States Fish and Wildlife Service, United States Department of the Interior. Funding was provided by the National Marine Fisheries Service through several grants to the Alaska SeaLife Center and to the North Pacific Universities Marine Mammal Research Consortium through the North Pacific Marine Science Foundation. Funding was provided to the National Marine Mammal Laboratory, Alaska Fisheries Science Center, by NOAA Fisheries. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.