Harem bulls on St. Paul Island decreased by 

 10.9 percent of the 1962 count; those on St. 

 George Island decreased by 11.6 percent. The 

 total number of harem bulls on the Pribilof 

 Islands was 89 percent of the 1962 count. 



The idle bulls on St. Paul Island showed a 

 decrease of 16 percent; those on St. George 

 Island decreased by 28.7 percent. The total 

 number of idle bulls on the Pribilof Islands 

 was 18.9 percent less than the count in 1962. 



Counts of harem and idle bulls were made 

 on East Rookery, St. George Island, at inter- 

 vals ranging from 4 to 7 days from 6 July to 

 16 August. The counts are given in table 5. 



Table 5. --Counts of harem and idle bulls, East 

 Rookery, St. George Island, 6 July to 

 16 August 1963 



classes, and a possible rise in pregnancy 

 rates, particularly among 3- and 4-year-old 

 females. Three- and four-year-old females 

 born on western Pacific islands currently 

 have much higher pregnancy rates than do 

 those born on the Pribilof Islands. The actual 

 yield of females may be appreciably less than 

 30,000 when calculated from more recent 

 data. 



Over 34,000 of the females killed on the 

 Pribilof Islands during the period 1956-62 

 were examined, and their general reproduc- 

 tive conditions correlated with age. Each 

 female was classified as nulliparous, primi- 

 parous, or multiparous, depending upon 

 whether she had given birth to none, one, or 

 two or more pups in her lifetime. Her current 

 reproductive condition (post partum or nonpost 

 partum) was also noted. The principal objec- 

 tive was to establish pregnancy rates by age 

 class and for breeding-age females as a group. 

 The problem of determining what proportion 

 of females from the rookeries and what pro- 

 portion from the hauling grounds would con- 

 stitute a mixture representative of all the 

 females has not been solved. Nearly 100 

 percent of the females taken from the rook- 

 eries during the peak of breeding (July) were 

 pregnant when examined or had given birth a 

 few days before. In contrast, as few as 21 

 percent of the females found on the hauling 

 grounds in August had borne pups in the year 

 examined. No changes in general reproductive 

 condition of females taken on land from 1956 

 to 1962 have been observed. 



FEMALES 



A total of 270,054 females have been taken 

 on land since inception of the herd reduction 

 program in 1956. The land kill, plus an addi- 

 tional unknown number of females eliminated 

 through natural mortality, presumably has 

 resulted in an appreciable decrease in the 

 number of pups born. Intermittent herd reduc- 

 tion, however, has made it difficult to detect 

 any influences that removal of females may 

 have had so far. Had it been practical and 

 economical, elimination of 250,000 females 

 the first year (1956) would have provided a 

 starting point from which various factors 

 could have been traced more accurately. 

 Weaknesses in the tagging program have also 

 contributed to inaccuracies because associated 

 errors tend to inflate population estimates. 



It was calculated that the herd, when re- 

 duced to and kept at a certain level below its 

 peak, will produce a maximum annual sus- 

 tained yield of 60,000 males and 30,000 females 

 harvested for their skins. The maximum 

 sustained yield is expected to result from 

 reduced mortality of the young, elimination of 

 wide fluctuations in survival of the year 



Methods Used in Current Studies 



Unlike those age 5 and older, 3- and 4-year- 

 old females taken in the kill may be repre- 

 sentative of all females of these ages present 

 on land because they do not begin to appear on 

 the Pribilof Islands until early August or about 

 2 weeks after the peak of breeding. Also, 

 because most 3- and 4-year-old females have 

 yet to give birth to their first pup, they are 

 free to wander between the rookeries and 

 hauling grounds. Thus, females of these ages 

 are perhaps representative of their respective 

 age classes regardless of where they are 

 collected. For these reasons, studies of females 

 were modified in 1963 to include a detailed 

 analysis of reproductive activity of known-age 

 3- and 4-year-old females taken in the kill. 



Sampling of the kill was continued for age 

 classification, and teeth were processed as in 

 the past, except that those age 8 and older 

 were grouped as age 8 + . Teeth in this group 

 will be sectioned later, and the ages read 

 internally. In other years, ages were read 

 externally through age 10; those 11 and older 

 were grouped as 10+ and sectioned later. 



The females used for studies of reproduc- 

 tion were also weighed and their body lengths 

 recorded. A behavior study begun on a section 



