The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . easternberingsea00hood Year: 1981 Northern fur seals 849 \ through 1968, the annual female take was restricted to the number calculated as exceeding losses from natural causes. Consequently, the harvest of females during this period was considerably reduced from that of 1956-63. The intentional harvest of females was stopped after 1968, because the male harvest was not in- creasing as expected after several years of pup pro- duction at the 1963 level. In 1973 the commercial harvest on St.
The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . easternberingsea00hood Year: 1981 Northern fur seals 849 \ through 1968, the annual female take was restricted to the number calculated as exceeding losses from natural causes. Consequently, the harvest of females during this period was considerably reduced from that of 1956-63. The intentional harvest of females was stopped after 1968, because the male harvest was not in- creasing as expected after several years of pup pro- duction at the 1963 level. In 1973 the commercial harvest on St. George Island was suspended, and efforts were made to obtain information on factors which regulate population size. The present man- agement policy for the herd on St. Paul Island is to harvest only males exceeding the number required for an adequate population of breeding males. No females are taken. This policy is expected to allow the St. Paul herd to reach carrying capacity. CHANGES IN POPULATION CHARACTERISTICS When the herd reduction began, the birth rate was expected to increase and the death rate from natural causes after birth to decrease, resulting in a larger harvest. No data on birth rate are available, but analysis of the and Canadian pelagic catch of fur seals (for research) from 1958 to 1974 yielded information on average age at first pupping and age- specific pregnancy rates. Separate analyses of the pelagic data (Kajimura et al. 1979) show neither a substantial decrease in age at first pregnancy nor an increase in pregnancy rates as the population was reduced. In fact, some data suggest that among females from four to six years old the pregnancy rate may have declined during the period of analysis. Lander (1979) computed survival rates of pups on land before migration and during the first 20 months at sea for the 1950-70 year-classes. Using these survival estimates, we find that male pup mortality on land and for the first two years of life decreases with
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