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 leve l for the northern fur seal (Callorhinus ursinus) population of St. Pa ul Island, Alaska. Definitive determination of this level is not possi ble due to uncertainty in life table parameters and density-dependent changes in those parameters. To account for such uncertainty, repetiti ve numerical simulations were used to generate frequency distributions of estimates for the maximum net productivity level and related popul ation parameters. This approach systematically varied simulation input parameters, ran a separate simulation with each input parameter combi nation, and validated the simulations on the basis of comparison with historical observations. Results from validated simulations were compi led in frequency distributions to provide a measure of confidence for MNPL estimates. The distributions confirm that this population is prob ably well below its maximum net productivity level. Because they refle ct the uncertainty in our understanding of northern fur seal populatio n dynamics, these distributions are a more realistic basis for managem ent than single point estimates.