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The Decline of the Steller Sea Lion in the Northeast Pacific: Demography, Harvest or Environment?

Pascual, Miguel A., Adkison, Milo D.
Ecological applications 1994 v.4 no.2 pp. 393-403
Eumetopias jubatus, demography, fish, harvesting, mammals, population dynamics, pups, stochastic processes
When apparent declines in population numbers are observed, biologists are confronted with the challenge of determining if such behavior conforms to the expected dynamics of the population or if, on the contrary, the decline reflects some pathological change in the environment that requires management actions. Experimental investigations are often impractical for large free—ranging populations such as fish or large mammals. Consequently, biologists need to get the best possible answer from the limited data available. In this paper we combine deterministic and stochastic modeling, together with statistical estimation techniques, to explore the likelihood of various hypotheses for the decline of Steller sea lions in the North Pacific. Our results show that deterministic transient population behavior, historical pup harvesting, and short—term environmental stochasticity are unlikely causes for the decline. The elimination of these alternatives leads us to agree with previous authors, who suggest that some long—term change in the environment or a novel catastrophe is responsible for the decline.