Regional differences in the spatial and temporal heterogeneity of oceanographic habitat used by Steller sea lions

Over the past three decades, the decline and altered spatial distribution of the western stock of Steller sea lions (Eumetopias jubatus) in Alaska have been attributed to changes in the distribution or abundance of their prey due to the cumulative effects of fisheries and environmental perturbations. During this period, dietary prey occurrence and diet diversity were related to population decline within metapopulation regions of the western stock of Steller sea lions, suggesting that environmental conditions may be variable among regions. The objective of this study, therefore, was to examine regional differences in the spatial and temporal heterogeneity of oceanographic habitat used by Steller sea lions within the context of recent measures of diet diversity and population trajectories. Habitat use was assessed by deploying satellite-depth recorders and satellite relay data loggers on juvenile Steller sea lions (n = 45) over a five-year period (2000–2004) within four regions of the western stock, including the western, central, and eastern Aleutian Islands, and central Gulf of Alaska. Areas used by sea lions during summer months (June, July, and August) were demarcated using satellite telemetry data and characterized by environmental variables (sea surface temperature [SST] and chlorophyll a [chl a]), which possibly serve as proxies for environmental processes or prey. Spatial patterns of SST diversity and Steller sea lion population trends among regions were fairly consistent with trends reported for diet studies, possibly indicating a link between environmental diversity, prey diversity, and distribution or abundance of Steller sea lions. Overall, maximum spatial heterogeneity coupled with minimal temporal variability of SST appeared to be beneficial for Steller sea lions. In contrast, these patterns were not consistent for chl a, and there appeared to be an ecological threshold. Understanding how Steller sea lions respond to measures of environmental heterogeneity will ultimately be useful for implementing ecosystem management approaches and developing additional conservation strategies.

Studies on the Helminth Fauna of Alaska. XIII. Disease in the Sea Otter, with Special Reference to Helminth Parasites

During the spring of 1951, the U. S. Fish and Wildlife Service undertook the removal of sea otter, Enhydra lutris (L)., from the Aleutian Island of Amchitka, for the purpose of restocking range from which the animals have long been exterminated. The decision to undertake this activity was influenced by the nature of military operations planned for the island later the same year. The capture and removal of the otter were under the supervision of Mr. Robert D. Jones, Biologist, U. S. Fish and Wildlife Service. Heavy losses among the animals shortly after capture made the venture unsuccessful. Many deaths were concurrent among animals in the wild state. The writer was asked to investigate the causes of disease in the sea otter, and it is the purpose of this paper to report the results of these investigation, with special reference to helminth parasites.