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Resource partitioning by sympatric Steller sea lions and northern fur seals as revealed by biochemical dietary analyses and satellite telemetry
Ist Teil von
Journal of experimental marine biology and ecology, 2012-04, Vol.416-417, p.41-54
Ort / Verlag
Elsevier B.V
Erscheinungsjahr
2012
Link zum Volltext
Quelle
Elsevier ScienceDirect Journals Complete
Beschreibungen/Notizen
Over 1000 endangered Steller sea lions (SSL, Eumetopias jubatus Schreber, 1776) and approximately 14000 northern fur seals (NFS, Callorhinus ursinus L., 1758) breed sympatrically at the Lovushki Island complex, located in the northern Kuril Island chain in the Russian Far East, creating the potential for inter-specific competition for prey resources. The diets and foraging locations of both species were examined through the analysis of δ15N and δ13C stable isotope (SI) ratios of vibrissae, fatty acid (FA) profiles of blubber biopsies, and telemetry data collected during the breeding seasons of 2007 and 2008. There were significant differences in the mean δ15N and δ13C values between SSL and NFS. Adult female SSL were significantly enriched in both δ15N and δ13C over adult female NFS (by 2.04‰±0.23‰ and 0.83‰±0.12‰, respectively), which indicates that the sea lions were feeding at a higher trophic level and in a different geographical location than the fur seals. The higher mean δ13C levels found in the sea lion vibrissae suggest that they fed nearshore and benthically, while fur seals fed primarily offshore and pelagically. There were significant differences in the blubber FA profiles between SSL and NFS, indicating that the two species have different foraging strategies with respect to the types and/or proportions of prey items consumed. Foraging behavior analysis also indicated that SSL foraged nearshore and benthically and breeding NFS foraged primarily offshore and pelagically. The combination of these methodologies suggests breeding NFS and SSL partition their forage resources by prey type, as well as spatially, which likely reflected the differences in provisioning strategies of the adults and the fasting abilities of their pups.
► We examine the diets of sympatric Steller sea lions and northern fur seals. ► Stable isotopes and fatty acids indicate significant dietary differences. ► Telemetry and stable isotopes indicate foraging grounds are spatially partitioned. ► Partitioning of forage resources may reduce inter-specific competition for prey. ► Differences may reflect adult provisioning strategies and pup fasting abilities.