Shipboard surveys were conducted along the Aleutian Islands in 2001 and 2002 to assess the influence of a suite of biophysical parameters on regional patterns in the distribution of cetaceans and Steller sea lions (SSL; Eumetopias jubatus). Distributions of four large whale species: fin (Balaenoptera physalus), humpback (Megaptera novaeangliae), minke (B. acutorostrata) and sperm (Physeter macrocephalus) aligned with proposed metapopulation breaks in diet and population trend of SSLs. Dall's porpoise (Phocoenoides dalli) and killer whales (Orcinus orca) were widely distributed throughout the study area, and killer whales were particularly prevalent along the north Aleutian Island coastlines between Unimak Pass and Samalga Pass. Biopsies determined that most killer whales (92%) were of the piscivorous (resident) ecotype as opposed to the mammal-eating (transient) ecotype observed in 2002 only. Generalized additive models (GAMs) were used to explore relationships between these multispecies patterns in distribution, oceanographic variables (salinity, temperature, fluorescence and depth) and proximity to six Aleutian passes. The GAMs indicated the best-fit models and most significant correlations as determined by the Akaike function and Cp-statistics were: depth and proximity to the nearest measured pass for SSLs and all cetaceans, respectively; frequencies of herring and salmon in SSL diet with population trend; fluorescence in the top 50 m with occurrence of humpback, minke, and killer whales; and surface temperature with occurrence of humpback, killer, and sperm whales. Results of the GAM analyses suggest foci for future investigation of relationships between physical variables and interspecific patterns of marine mammal distribution.
Scats (fecal samples) collected between 1987 and 2000 on northern fur seal Callorhinus ursinus rookeries of St Paul (n= 2968) and St George Islands (n = 1203), Alaska, were used to examine the relationship between breeding sites and food habits of adult female seals. On the basis of the frequency of occurrence (FO) and per cent minimum number of individual prey (%MNI) in scats, juvenile walleye pollock Theragra chalcogramma and gonatid squid Gonatopsis borealis/ Berryteuthis magister and Gonatus madokai/Gonatus middendorffi were the dominant prey species consumed overall. Other primary prey (FO45%) included Pacific sand lance Ammodytes hexapteus, Pacific herring Clupea pallasi, northern smoothtongue Leuroglossus schmidti, Atka mackerel Pleurogrammus monopterygius, Pacific salmon (Oncorhynchus spp.) and other squid of the Gonatus genus. We identified five rookery complexes from a cluster analysis of the FO of primary prey in scats. Rookery complexes were separated geographically and each was further defined by characteristic patterns in the representation of prey types typically associated with specific hydrographic domains. Diet differences were observed among rookeries on the north and south side of St George Island and on the east, south and south-west side of St Paul Island. The rookery clusters observed in this study provide evidence of resource partitioning among adult female northern fur seals and have important implications for fur seal conservation and management.
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