Timothy J. Ragen

Early Migration of Northern Fur Seal Pups from St. Paul Island, Alaska

The early migration of northern fur seal ( Callorhinus ursinus ) pups was investigated using very high-frequency (VHF) radiotelemetry. In 1989–1990, 184 pups were radiotagged and monitored to determine the date of their departure from St. Paul Island, Alaska. After their departure, 70 pups were located by receiver stations in the eastern Aleutian Islands and by aerial surveys. Mean (±1 SD ) time of travel between St. Paul Island and the Aleutian passes was 11 ± 6 days ( n = 63), suggesting that, on average, pups progressed southward at the rate of ca. 36–40 km/day. Near the Aleutians, they were distributed throughout the study area from Unimak Pass to Samalga Pass, and Unimak Pass was not the main migratory route from the Bering Sea into the North Pacific Ocean. The pups remained dispersed as migration continued south of the Aleutian Islands. The migratory routes of northern fur seal pups in the Bering Sea and North Pacific Ocean have important implications for their pelagic ecology, including the type and availability of prey, oceanographic conditions encountered, population dynamics (e.g., survival and reproductive recruitment), and potential for interaction with human activities.

A Review of Northern Fur Seal Population Modelling

Population models are reviewed to reveal trends in the study and management of the northern fur seal (Callorhinus ursinus) population of St Paul Island, Alaska. These trends include: (1) increasing model complexity, (2) recognition of the nonlinear nature of density-dependent population regulation, (3) extension of density-dependent effects to vital rates other than juvenile survival, and (4) growing emphasis on adequacy of models through validation and sensitivity analysis. Although these trends demonstrate progress in our understanding of northern fur seal population regulation, they also emphasize limits to that understanding. The implications of these limits are considered with respect to future management and study of northern fur seal populations.