Prey competition between sympatric Steller sea lions (Eumetopias jubatus) and northern fur seals (Callorhinus ursinus) on Lovushki Island, Russia
Approximately 1 000 Steller sea lions (Eumetopias jubatus (Schreber, 1776); SSL) and 14 000 northern fur seals (Callorhinus
ursinus (L., 1758); NFS) breed sympatrically on Lovushki Island in the Russian Far East, creating the potential for interspecific competition for prey. An additional 13 000 – 14 000 juvenile NFS are present during the breeding season. The
diets of breeding SSL and both breeding and juvenile NFS were examined through analysis of scats and spews collected during the breeding seasons of 2003, 2005, and 2007–2008. There were significant overlaps in the prey species and size selection of SSL and juvenile NFS. There were significant
differences between the diets of SSL and breeding NFS. SSL and juvenile NFS fed primarily on Atka mackerel (Pleurogrammus monopterygius (Pallas, 1810)), while breeding NFS fed on cephalopods, salmon
(genus Oncorhynchus Suckley, 1861), Atka mackerel, and northern smoothtongue (Leuroglossus schmidti Rass,
1955). The partitioning of resources between breeding animals has allowed both species to coexist within the same region and likely reflected differences in foraging abilities and provisioning strategies of the adults and the fasting abilities of their pups. However, continued growth of the
NFS population may lead to the exclusion of SSL owing to interspecific competition for prey.
Document Type: Research Article
School of Fisheries and Ocean Sciences, University of Alaska, 905 North Koyukuk Drive, 245 O’Neill Building, Fairbanks, AK 99775, USA.
National Marine Mammal Laboratory, National Oceanic and Atmospheric Administration (NOAA), 7600 Sand Point Way NE, Seattle, WA 98115, USA.
Publication date: January 5, 2012
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