MAXIMUM NET PRODUCTIVITY LEVEL ESTIMATION FOR THE NORTHERN FUR-SEAL (CALLORHINUS-URSINUS) POPULATION OF ST-PAUL ISLAND, ALASKA

The goal of this study was to assess the maximum net productivity level for the northern fur seal (Callorhinus ursinus) population of St. Paul Island, Alaska. Definitive determination of this level is not possible due to uncertainty in life table parameters and density-dependent changes in those parameters. To account for such uncertainty, repetitive numerical simulations were used to generate frequency distributions of estimates for the maximum net productivity level and related population parameters. This approach systematically varied simulation input parameters, ran a separate simulation with each input parameter combination, and validated the simulations on the basis of comparison with historical observations. Results from validated simulations were compiled in frequency distributions to provide a measure of confidence for MNPL estimates. The distributions confirm that this population is probably well below its maximum net productivity level. Because they reflect the uncertainty in our understanding of northern fur seal population dynamics, these distributions are a more realistic basis for management than single point estimates.