Fur Seal Investigations 

 Pribilof Islands, Alaska, 1963 



By 



ALTON Y. ROPPEL, ANCEL M. JOHNSON, 

 and DOUGLAS G. CHAPMAN 



ABSTRACT 



Of 42,386 male seals killed on the Pribilof Islands in 1963, 39,685 were taken 

 during the male kill from 2 July to 5 August and 2,701 during the kill of females 

 13 August to 12 September. Age classification in percent was: 5, 45, 45, and 5, 

 for ages 2, 3, 4, and 5. At least 3,150 male seals were taken as a result of early 

 season removal of the maximum length limit of 48-3/4 inches. The peak of the kill 

 occurred 22-26 July. The kill of 18,481 4-year-old males by 5 August agreed with 

 the forecast of 18,750. A kill of 37,500 3-year-old males by 31 July was predicted; 

 17,986 were taken by 5 August. The forecast for 1964 is 50,000 males by 5 August. 

 Harem and idle bulls counted were 11,283 and 9,540. Based on tag recoveries from 

 males ages 3 and 4, the number of pups born in 1958 and 1959 were 729,000 and 

 778,000; from female data, the estimates were 872,376 and 859,371. Based on 

 marked to unmarked ratios obtained from shearing and sampling pups, the estimate 

 of the number of pups born on the Pribilof Islands in 1963 is 316,000. A total of 

 43,952 females were taken. Three- and four-year-old females seemed to return to 

 rookery areas rather than to hauling grounds as in the past. Reproductive studies 

 showed that 2 of 170 4-year-old females examined were primiparous and had given 

 birth to their first pup in 1963, that all (140) of the 3-year-old females examined 

 were nulliparous, and that 24 percent of the 3-year-olds and 70 percent of the 

 4-year-olds would have been bred in 1963. Because only 3 and 32 percent of the 4- 

 and 5-year-old females examined in 1962 had given birth to pups that year, many 

 3- and 4-year-old females apparently do not conceive or most of the fetuses carried 

 by young females die early in life. Recoveries of marked animals included 3,703 

 with tags, 2,077 with checkmarks only, 84 with tags attached in 1961 and 1962 to 

 animals presumed to be yearlings, and 37 with Soviet tags. Twenty-five thousand 

 seal pups and 701 yearlings were tagged. The heads of 21,919 seal pups were 

 sheared. Land pup mortality was 39,239. Surveys of yearlings tagged as pups in 1962 

 were made to provide an index to survival from birth to age 1. A correlation be- 

 tween mean weight as pups and return at age 3 is suggested. Tagged pups continue 

 to weigh less than untagged pups. The average difference was 0.57 kg. 



INTRODUCTION 



The fur seal populations in the North Pacific 

 seem to be almost ideal subjects for testing 

 population principles among large mammals. 

 A large part of the population is present at 

 one time on small islands, there is an inten- 

 sive harvest, and the seals can be marked 

 and measured. Further, there is good com- 

 munication between biologists of different 



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

 Biologists (Research), Bureau of Commercial Fisheries 

 Marine Mammal Biological Laboratory, U.S. Fish and 

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

 Laboratory of Statistical Research, University of Wash- 

 ington, Seattle, Wash. 



countries working on the different islands and 

 at sea. 



Allen (1954, p. 35 and 37) called attention 

 to some pertinent principles of population 

 management in the following statements : "Few 

 people appreciate the drastic waxing and waning 

 of animal numbers with the cycle of the sea- 

 sons. 



"We cannot manage or even harvest, . . . 

 to best advantage until we have a realistic 

 conception of the annual destruction and re- 

 placement of numbers. 



"Most large-scale errors in handling wild- 

 life resources have stemmed from a failure to 

 comprehend the forces at work in populations. 



