Population 



When the Convention of 1911 first gave inter- 

 national protection to fur seals, the Pribilof herd 

 numbered about 200,000 and could be counted 

 with reasonable success. After 1924, only bulls 

 were counted because crowding and constant inter- 

 change of animals on the rookeries made a mean- 

 ingful count impossible. Until 1948, the size of 

 the herd was estimated annually on the basis of 

 calculated geometric rates of increase established 

 just after the turn of the century. The calculated 

 and actual increase corresponded well until the 

 mid-1930's, but by 1947 the method was discon- 

 tinued because there was then no basis for cal- 

 culating the increase rate, with useful accuracy, 

 for a population that was near the peak of the 

 growth potential. The estimate of the number of 

 pups born in 1957 was 770,000. The total Pribi- 

 lof herd exceeds 1,500,000. The population on 

 all other North Pacific islands (Commanders, 

 Robben, Kuriles) is about 250,000 in late summer. 

 The herds on these islands have rates of increase 

 that are similar to the rate demonstrated by the 

 herd on the Pribilof Islands in the 1920's when 



it was growing rapidly. Seals on the western Paci- 

 fic islands have a better survival of pups and 

 higher reproduction rates among young females. 

 The change in growth rate as these herds mature 

 will be followed with interest by students of animal 

 population dynamics. 



Satisfactory management requires some mea- 

 sure of changes in various segments of the popu- 

 lation. These include number of pups born, 

 survival of year classes, number of bulls, preg- 

 nancy rates, and extent of mortality at various 

 ages. Marking of seals for management pur- 

 poses began in 1912. Since 1947 tagging has been 

 used as a means of estimating the population. 

 Over 500,000 seal pups were tagged between 1947 

 and 1962. The current rate of tagging is 50,000 

 per year. By combining ( 1 ) information from 

 tag recoveries, (2) age classification of the kill 

 through tooth growth- ring counts, (3) pregnancy 

 rates, and (4) pup mortality counts, annual est- 

 imates of the number of pups born are statistically 

 calculated. 



Management 



Fur seal habits are such that a program of 

 wise utilization is readily devised. The success 

 of such a program, however, depends on inter- 

 national cooperation because the seals live much 

 of the time outside territorial waters. In Alaska, 

 fur seals come ashore only on the Pribilof Islands, 

 always about the same date each year. Because 

 seals are highly polygynous and the sexes are born 

 in equal numbers, it is possible to take many males 

 without adversely affecting the productivity of 

 the herd. The young males, whose pelts are 

 most valuable, habitually haul out on the islands 

 apart froni the breeding animals in the harems, 

 so that little difficulty is experienced in obtaining 

 them. 



Harvesting of the seals is limited for the most 

 part to the 3- and 4-year-old males. In 1918, 

 age-length relationships were established by the 

 U. S. Government from measurements taken of 

 seals of known age, branded as pups in 1912. 

 Until recently this age-length relation has served 

 as the basis for estimating the age of animals 

 to be utilized commercially. The kills are now 

 classified into age categories by counting the an- 

 nular ridges on a 10-percent sample of canine 

 teeth. Also the range of lengths within ages 

 is more fully understood through extensive recent 

 measurements of tagged seals. 



From 1911 to 1917, seals were killed only for 



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