Fur Seal Investigations, 1968 



by 



NATIONAL MARINE FISHERIES SERVICE 

 MARINE MAMMAL BIOLOGICAL LABORATORY 

 Sand Point Naval Air Station 

 Seattle, Washington 98115 



ABSTRACT 



Field investigations in 1968 were made on the Pribilof Islands from June to 

 October, in Washington waters in November-December 1967 and January-February 



1968, and in Alaska waters fronn May to August 1968, Data were collected during 

 these periods for studies of population levels and the maxin-ium sustained yield, 

 and the distribution, feeding habits, migrations, and pregnancy rates of fur seals. 



In 1968, 45,625 male and 13,335 fen-iale fur seals (Callorhinus ursinus) were 

 killed on the Pribilof Islands. 



Dead fur seals counted included 31,438 pups and 350 animals older than pups. 



The major causes of death among 379 pups were malnutrition, hookworna di- 

 sease, trauma, infections, and perinatal complex. 



We estimated that the Islands had 7,924 harem and 4,383 idle males in mid-July. 



Pregnancy rates of females were 42 percent for 1,058 from hauling grounds in 

 1968 and 100 percent for 221 from rookeries in 1957. 



The average weights of the pups were 9.6kg. for males and 8.3 kg. for females. 



Seals tagged included 11,675 pups regardless of sex, 714 males estimated to be 

 yearlings, and 1,495 males estimated to be 2 years old. 



Of the marked seals recovered, 3,946 had been given tags or other marks as 

 pups and 1,197 had been tagged at age 1 or older. 



Tag loss apparently is highest soon after tagging. 



The recovery rate for pups tagged in September has been higher than that for 

 pups tagged in August. 



Pups marked by removing parts of flippers apparently have a higher survival 

 rate than pups that have been given tags and flipper n-iarks. 



Two different methods of estimating populations yielded similar values (400,000 

 and 350,000) for the number of pups born in 1965. The pup population estimates de- 

 creased annually since 1960 to less than 400,000 in 1965, 



Estimates of the number of yearling males for several year classes are 82,000 

 (1961), 79,000 (1962), 115,000 (1964), and 80,000 (1965). 



After the kill in 1 966, the population still included 25,000 3-year-old males from 

 the 1963 year class and 70,000 2-year-old males from the 1964 year class. 



The predicted kill of males in ages 2 to 5 was 49,000 for 1968 and is 56,000 for 



1969. The actual kill in 1968 was 44,162. 



The recovery rate of young males tagged and recovered in 1968 was higher for 

 those marked in June than for those marked in July. The recovery rate for seals 

 tagged on hauling grounds inaccessible to the kill was less than that for seals 

 tagged on accessible hauling grounds. One of ten transmitters attached to seals 

 emitted signals for 9 days. 



Nearly all of 250 adult nnales killed from rookeries were age 10 or older, but 

 58 percent of 100 adult males killed from hauling grounds were less than 10 years. 



Researchers took 374 seals off Washington and 456 in Alaska waters; 38 of these 

 seals had tags or other marks. About 50 percent of the female seals taken were from 

 1 to 7 years old. 



The principal fishes eaten by fur seals off Washington were salmon, Oncorhyn- 

 chus spp.; anchovy, Engraulis mordax ; rockfish, Sebastodes spp.; eulachon, 

 Thaleichthys pacificus ; and capelin, Mallotus villosus . The principal foods consumed 

 in Alaska waters were walleye pollock, Theragra chalcogrannnnus ; squids. 

 Cephalopoda; and Atka mackerel, Pleurogrammus monopterygius. 



