The term "optimum sustainable population" has been defined 

 as a range of population levels between the largest supportable 

 within the ecosystem (i.e. , carrying capacity) and the 

 population level that results in the greatest net annual 

 increment in population numbers or biomass due to population 

 reproduction or growth (i.e. , maximum net productivity) . The 

 maximum net productivity level for fur seals has not been 

 estimated, but, based on precedents established for other 

 species, would be 60 percent or more of carrying capacity. 

 As indicated above, the estimated size of the Pribilof Islands' 

 fur seal population in 1983 (871,000 animals) was about 40 

 percent of the estimated size in the 1940s and early 1950s 

 (2.2 million animals). 



As discussed in previous Annual Reports, the Marine 

 Mammal Commission, in consultation with its Committee of 

 Scientific Advisors on Marine Mammals, recommended in 1984 

 and again in 1985 and 1986 that the National Marine Fisheries 

 Service formally designate the Pribilof Islands' population of 

 North Pacific fur seals as depleted under the Marine Mammal 

 Protection Act. On 30 December 1986, the Service published 

 and requested comments on a proposed rule to do so. The 

 comment period, initially scheduled to end early in February 

 1987, was extended to the end of March to accommodate rural 

 Alaskans. 



The Commission provided comments to the Service on 6 March 

 1987, concurring with the proposed action. Among other things, 

 the Commission noted that while the population had declined 

 to less than 50 percent of its level in the 1940s and early 

 1950s, there is no evidence suggesting that the North Pacific 

 ecosystem cannot still support a fur seal population as high 

 as was observed during that earlier period. In this regard, 

 it noted that the average body sizes of both male and female 

 fur seals had increased and the length of time fur seals 

 spend at sea feeding had decreased, suggesting that the 

 population was not being limited by decreased food supplies. 



On 4 August 1987, the Service requested comments from the 

 Commission and others on a draft final rule designating the 

 Pribilof Islands' fur seal population as depleted. During 

 consideration of the draft rule, the Service's Northwest and 

 Alaska Fisheries Center questioned the Service's determination 

 that the fur seal's carrying capacity had not changed 

 significantly since the peak population size in the early 

 1950s. In response to the Center's questions, the Service 

 suspended action on the proposed rulemaking and reopened the 

 comment period on the proposed rule on 31 December 1987. In 

 doing so, it requested new information on possible changes in 

 the carrying capacity of the Bering Sea ecosystem. The comment 

 period closed 29 February 1988. 



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