NOAA Technical Memorandum
NMFS-AFSC-46
Fur seal investigations, 1993
Abstract
This report is a collection of papers that describe the 1993 research activities of the National Marine Mammal Laboratory on northern fur seals (Callorhinus ursinus).
Counts of adult male fur seals were conducted on the Pribilof Islands in the eastern Bering Sea in mid-July. A total of 18,251 adult male seals were counted, which is 5.25% less than the number counted in 1992, suggesting that the recently observed annual increase in male counts following the 1984 cessation of commercial harvesting of subadult males is subsiding.
Estimates of survival of the 1987 and 1988 cohorts of juvenile male northern fur seals tagged on St. Paul Island demonstrates the feasibility of obtaining estimates of male northern fur seal survival from tag returns. However, the level of precision in the estimates needs to be further refined.
An assessment of error in condition index measurements conducted on St. Paul Island in 1992 indicates that both length and weight are useful parameters in evaluating the condition of northern fur seal pups. The number of northern fur seal. pups counted on San Miguel Island, California, conducted in late July (n = 2,045) was higher than in any year since the colony was discovered in 1968. However, mean pup weights were significantly lower than weights recorded in non-El Niño years.
A total population count was conducted on Bogoslof Island in the south central Bering Sea on 23 August. This was the first census since 1990 and the first since the northeast end of the island erupted in 1992. A total of 5,536 live fur seals were counted, 890 of which were pups. Counts from 1992 and 1990 can not be directly compared since the 1990 census was conducted in July when aggression by territorial bulls makes it difficult to accurately count all areas (Baker and Kiyota 1992). The latest counts, however, appear to represent a near fourfold increase in population numbers since 1990.
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