Uncertain management or management of uncertainty: Steller sea lion—a case study
R.J. Small, and D.P. DeMaster
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The abundance of Steller sea lions (sea lions) declined ~15% per year during the 1980s in the Bering Sea, Aleutian Islands, and Gulf of Alaska regions, resulting in a threatened listing under the Endangered Species Act (ESA) in 1990. Numerous factors may have contributed to the decline, and there has been substantial uncertainty regarding the relative impact of these factors when management actions were implemented to promote recovery. One key hypothesis for the continued decline in the 1990s (~5%/year) has been a reduction in sea lion prey biomass and quality caused by either commercial fishing or an "oceanographic regime shift" resulting in substantial changes in the abundance or availability of dominant prey species, which may have subsequently resulted in nutritional stress on the sea lion population. Following the 1997 ESA endangered listing of the western population and the determination that competition with commercial groundfish fisheries in Alaska was likely, additional fishery management restrictions were implemented. Counts of sea lions in 2002 and 2004 indicate the decline of sea lions may have begun to cease. The evidence for nutritional stress, especially post-1990, is somewhat contradictory and equivocal which contributes to continued uncertainty. Given the ESA’s mandate to U.S. federal regulatory agencies to manage in a strongly precautionary manner, greater uncertainty can be translated to mean more precautionary management. To address ongoing uncertainty about causal factors and the efficacy of conservation actions, we believe that a research strategy with four primary components should be pursued: (1) population monitoring and fundamental sea lion ecological research, (2) fishery interaction studies designed to test the localized depletion hypothesis, (3) determining the mechanism by which changes in prey biomass or nutritional quality of the prey species may result in chronic nutritional stress that results in decreased sea lion survival and reproduction, and (4) adaptive management experiments to assess the impact of fisheries on the sea lion prey field and subsequently sea lion demography. In addition, recently suggested modifications to conservation policy should be pursued: (a) establishing a specific quantitative standard for risk of extinction (under the ESA), (b) defining jeopardy and adverse modification of critical habitat (under the ESA) in terms of risk of extinction, and (c) establishing a quantitative standard for ecosystem protection in developing recovery strategies for ESA listed species. Implementation of these research and conservation policy recommendations could substantially decrease uncertainty and increase the probability of effective conservation of sea lions.
- Item number: AK-SG-06-01af
- Year: 2006
- DOI: https://doi.org/10.4027/slw.2006.32