TABLE 5. — Predicted and actual kill of male seals, Pribilof Islands, Alaska, 



1962 



of 22.7 percent, while the number on St. George 

 Island increased 6.5 percent. 



Because bull counts are made but once an- 

 nually on the Pribilof Islands, substantial 

 differences between two successive years do 

 not necessarily reflect an actual change in 

 numbers, except on land. For example, large 

 numbers of idle bulls have been observed to 

 disappear from the hauling grounds and rookery 

 fringes within a relatively short period of 

 time, only to return just as quickly. A be- 

 havior study begun in 1961, but not yet com- 

 pleted, relates heavy rainfall and high air 

 temperature to the sudden movement of idle 

 bulls from land to sea. Females are affected 

 similarly. Although the departure and return 

 of the harem bull escapes cursory observation, 

 careful observations made during the present 

 behavior study show that the harem bull of the 

 Pribilof Islands is less of a permanent land 

 resident during the breeding season than for- 

 merly reported. 



Thus, the newly born pup crop is the only 

 herd element that can be found on land in its 

 entirety, and then only when most of the pups 

 have been born and before they begin to enter 

 the water. 



FEMALES 



The decision to bring the number of females 

 down to the calculated level of maximum 

 sustained yield has resulted in a total kill of 

 226,102 females on land during the 7-year 



period 1956-62. Herd reduction aimed toward 

 preventing the adverse effects of a peak 

 population was in progress only a year before 

 the herd began to display some of these ef- 

 fects. Mortality of pups on land had already 

 been increasing for several years. The most 

 obvious effect has been wide fluctuation in 

 survival of the year classes. Scarcely 18,000 

 males were killed at ages 2, 3, and 4 from 

 the record 496,000 male pups estimated to 

 have been born in 1956. In contrast, 1958 

 production of 376,000 male pups contributed 

 a total of 78,000 males to the kill at ages 2, 3, 

 and 4. 



That the number of females has been sub- 

 stantially reduced through the combined ef- 

 fects of natural mortality and commercial 

 killing seems apparent from field observa- 

 tions. However, population estimates through 

 the 1959 year class do not indicate that a re- 

 duction has been achieved. As recently as 

 1959, certain of the hauling grounds occupied 

 more surface area than at present. The fewer 

 females on the hauling grounds have allowed 

 Vegetation to advance into areas where the 

 activity of many animals formerly kept the 

 ground bare. 



An analysis of the relationship of time to 

 the number of females killed supports the 

 general observations. In 1956, 22,680 females 

 were taken on thePribilof Islands by 15 August. 

 Many additional females, particularly old ani- 

 mals, were spared because the coincidental 

 kill of 95,936 males severely taxed the island 



