Fur Seal Investigations, 

 Pribilof Islands, Alaska, 1965 



by 



ALTON Y. ROPPEL, ANCEL M, JOHNSON 

 RAYMOND E. ANAS, and DOUGLAS G. CHAPMAN 



ABSTRACT 



The age classification of 40,367 male fur seals ( Callorhinus ursinus ) killed on 

 the Pribilof Islands in 1965 was: age 2, 4 percent; age 3, 56 percent; age 4, 36 

 percent; and age 5, 4 percent. Theagesof 901 male seals were not determined. The 

 peak of the kill occurred 27-31 July. Predicted kills of 3- and 4-year-old nnales on 

 St. Paul Island were 33,000 and 16,000; actual kills to 9 August were 19,009 and 

 12,046. All 2-year-old males available 22-26 July on St. Paul Island were killed to 

 determine if abundance on land at age 2 is related to return of the year class at 

 age 3. To test the commercial value of their skins, 854 males larger and older in 

 appearance than those normally taken were killed. Harem and idle bulls counted on 

 the Pribilof Islands were 10,470 and 6,729. Of 10,432 females killed, St. Paul Island 

 contributed 7,530, and St. George Island, 2,902. Selective killing for young females 

 on St. Paul Island 23-27 August produced 88 percent in ages 2-5; nonselective killing 

 on St. George Island 16-27 August produced 64 percent in ages 2-5. Sixty-five 

 3-year-old females examined were nuUiparous; 1 of 51 4-year-old females was 

 primiparous and recently post partum. Recoveries of marked seals included 4,947 

 with tags or checkmarks applied in the year of birth, 238 selected and tagged as 

 yearlings in previous years, and 36 seals tagged by the U.S.S.R. Ten thousand pups 

 were single-tagged and checkmarked, and 20,087 were checkmarked only; 922 seals 

 were double-tagged as yearlings. Pup mortality on land was 46,308. On the basis of 

 tag recoveries from males and counts of dead pups, about 560,000 pups were born 

 on the Pribilof Islands in 1961 and 500,000 in 1962. On the basis of tag recoveries 

 from females, 344,107 pups were born in 1960, 527, 482 in 1961, and 337,012 in 

 1962. Marked-to-unmarked ratios yielded an estimate of 347,000 pups born on the 

 Pribilof Islands in 1965. From tags recovered in 1965 from seals tagged as 

 yearlings in previous years, we estimated that there were 78,000 yearling males 

 in 1961 and 85,000 in 1962. The average weight of untagged and unmarked seal 

 pups exceeded that of tagged and marked seal pups by 1.14 kg. (males) and 1.04 kg. 

 (females). The predicted kill of male seals on St. Paul Island in 1966 includes 

 3,000 of ages 2 and 5, 26,000 of age 3, and 14,000 of age 4. Female seals will not 

 be purposely killed in 1966. 



INTRODUCTION 



Two recent advances in research are im- 

 portant for nnanagement of fur seals (Cal- 

 lorhinus ursinus ) on the Pribilof Islands. 

 First, we are making better estimates of the 

 number of pups born, the number of females 

 required to bear these pups, and the number 



Note. — Alton Y. Roppel and Ancel M. Johnson, Wildlife 

 Biologists (Research), and Raymond E. Anas, Fishery 

 Biologist (Research), Bureau of Commercial Fisheries 

 Marine Mammal Biological Laboratory, U.S. Fish and 

 Wildlife Service, Seattle, Wash. 98115; and Douglas G. 

 Chapman, Laboratory of Statistical Research, University 

 of Washington, Seattle, Wash. 98105. 



of feniales needed each year to replace those 

 that die. Second, we are studying the value 

 of finished sealskins by age and sex. 



Estimates of the number of pups born based 

 on the tag-and-recovery method have long 

 been known to be inflated, mainly as a result 

 of tag-induced mortality and loss of tags. 

 Additional pups are now marked each year by 

 shearing a patch of fur, and estimates of the 

 number born are obtained by sampling for a 

 marked-to-unmarked ratio 1 to 3 weeks later. 

 The estimates from shearing were sinnilar 

 to complete counts of pups on several small 

 rookeries. 



By applying to the pup estimates the preg- 

 nancy rates and mortality of seals obtained by 

 pelagic sampling, we can estimate the number 



