Entanglement studies, St. Paul Island, 1990 : juvenile male northern fur seals
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Entanglement studies, St. Paul Island, 1990 : juvenile male northern fur seals
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    During JuIy and early August of 1991, studies of the entanglement of juvenile male northern fur seals (Callorhinus ursinus) in marine debris were conducted on St. Paul Island, Alaska, in the Bering Sea. Seals from 101 roundups were sources of data for providing estimates of entanglement-caused mortality and incidence of entanglement. Other data were collected on the kinds and sizes of debris. The observed proportion of seals entangled in 1991 was less than that observed during the last several years and lower than that recorded during the commercial harvest and roundups from 1967 to 1986. The proportion of juvenile males observed entangled in 1991was 0.2l%. This rate reflects the continued reduction in the numbers of animals entangled in fragrments of trawl webbing. The frequency of occurrence of trawl webbing among the entangling debris in 1991 was about half that observed for 1990 and the levels for 1990 were about half those of earlier Ievels. In contrast, the proportion of seals entangled in other types of debris did not change. These studies confirm earlier estimates indicating that after 1 year, seals entangled in small debris (Iight enough to permit the animals to return to land) are reduced to about half the number expected had t.hey not been entangled. There is continuing evidence from the 1991 studies that the rate of return (survival) of tagged seals from which debris is removed. is significantly higher than for tagged seals on which entangling debris was left.
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