Decline of the Steller Sea Lion in Alaskan Waters Untangling Food Webs and Fishing Nets (2003) / Chapter Skim
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Executive Summary
Executive Summary
Pages 1-13
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There is no widely accepted answer to the question of why the Steller sea lion population is declining. What might otherwise be an obscure ecological mystery has become an issue of great regional and even national interest because of the regulatory implications for management of the large commercial fisheries in the North Pacific.
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The case of the dramatic decline in the Steller sea lion population has been less straightforward. Steller sea lions have not been subject to large commercial harvests since 1972, and the take of sea lions by fisheries has been estimated to be small relative to the size of the population.
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Therefore, if a federally regulated activity may affect Steller sea lions, the responsible agency must take actions to ensure that negative impacts are avoided. This requirement has made it imperative to identify human activities that may contribute to the decline of Steller sea lions so that regulatory actions can be adjusted to address threats to the western population's survival.
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Resolution of this conflict requires management that not only improves chances for the recovery of Steller sea lions but also facilitates scientific study of the efficacy of these protective measures. MAKING THE MOST OF EXISTING INFORMATION The hypotheses proposed to explain the decline of the western stock fall into two categories.
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Second, the evidence can be sorted geographically. In 1995 the National Oceanic and Atmospheric Administration determined that Steller sea lions west of 144° W constituted a distinct population unit based on dispersal patterns, population trends, and genetic differentiation.
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Finer-scale spatial analysis of Steller sea lion populations
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is the primary concern of this report because of the need to provide scientific advice for the design of management actions that do not jeopardize the continued survival of the western Steller sea lion population. Although limited in sample size, geographic range, and seasonality, recent measurements of sea lion condition and foraging activity indicate that the western stock is not nutritionally stressed and that individuals are not spending a disproportionate amount of time or energy in locating prey.
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Investigations of top-down sources of Steller sea lion mortality should be increased to evaluate the proportionate impact of these factors on the population decline. MONITORING TO EVALUATE MANAGEMENT EFFICACY Although most evidence indicates that groundfish fisheries are not causing a range-wide depletion of food resources necessary to sustain the current western population of sea lions, there is insufficient evidence to fully exclude fisheries as a contributing factor to the continuing decline.
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From page 9... ...
The closed treatment units would be subject to fishery closures, and the open units would have sea lion-related fishery restrictions removed. Under this option, the most critical monitoring needs would be detailed local Steller sea lion censuses and spatial analyses of fish population changes for each experimental unit in the overall design.
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Hence, the efficacy of new management restrictions would not be distinguishable from environmental change that occurs on decadal timescales, confounding either positive or negative outcomes. Second, a false positive outcome would commit managers to prolong additional fishery restrictions without realizing significant improvement in the survival of Steller sea lions.
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RECOMMENDATIONS FOR RESEARCH AND MONITORING Research and monitoring should be directed toward measuring the vital rates and response variables most indicative of the status of the Steller sea lion population. This should include
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Other parameters may be measured through increased effort in branding and relighting programs, requiring a commitment of resources for a period of time equivalent to the lifespan of the Steller sea lion. · Critical habitat.
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Hence, it is even more urgent to develop and implement a prioritized cohesive research plan to address these information needs. Under an adaptive management scheme, the requirement to reduce jeopardy can be effectively coupled with a rigorous research program to reduce uncertainty about the causes of the ongoing decline of the Steller sea lion population.
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