FISHERY BULLETIN: VOL. 84, NO. 2 



Table 1 .—Percent of each age included in standard length restrictions for kills of male 

 and female northern fur seals on hauling grounds. Percentages determined from Probit 

 plots of age-length cumulative length frequencies of seals collected at sea near St. 

 Paul Island by the United States and Canada. Sample sizes are in parentheses. 



1 Upper body size was the presence of a mane. A. Roppel (National Marine Mammal Laboratory, 

 National Marine Fisheries Service, NOAA, Seattle, WA 981 15, pers. comm. July 1983) felt that the 

 mane developed at a body length of about 135 cm. 



1). Numbers began to increase in early July and con- 

 tinued to increase up to 5 August. This age group 

 began to arrive earlier than the yearlings. Osgood 

 et al. (1915) observed the first branded 2-yr-old in- 

 dividuals on 12 June, about IV2 mo before the first 

 branded yearling males on rookeries. As found in 

 the current study, Kenyon and Wilke (1953) noted 

 that 2-yr-olds were quite common by the end of July, 

 and after 1 August became increasingly abundant. 



5000- 



4000 



3000 



2000- 



1000 



21 14 



^4 



a 2yr 

 • 3yr 

 O 4yr 



1 ,9,o /a '* ? n 



Figure 1.— Mean number, and standard error, of northern fur seal 

 males killed of age 2-4 on hauling grounds of St. Paul Island, by 

 date. Data from Lander (1980) and annual reports of the National 

 Marine Mammal Laboratory, Seattle. Number of years of data for 

 each date indicated above means. 



The date of peak numbers, and thus the date when 

 most arrived, was probably after early August. The 

 date when most would have arrived may be deter- 

 mined by assuming that the interval between the 

 time when seals clearly began to increase in number 

 and the time when essentially all seals had arrived 

 was the same for 2-yr-olds as for bulls and cows. 

 Observations by Peterson (1968) suggested that this 

 interval was about 1-1 V2 mo for bulls and pregnant 

 females. Because the number of 2-yr-old males 

 began to increase in early July, the arrival time for 

 most was probably mid- to late August. A similar 

 arrival time was also indicated by subtracting I-IV2 

 mo, the interval separating the first sightings of 

 tagged yearlings and 2-yr-olds, from the arrival time 

 of late September to early October for yearling 

 males on rookeries. 



The number of 2-yr-olds returning appeared to be 

 greater than that for yearlings, but less than that 

 for 3-yr-olds. Roppel (fn. 3) felt that more 2-yr-old 

 males returned than yearling males, and Kenyon et 

 al. (1954) noted that many 2-yr-olds remained at 

 sea. 



3-Year-Olds 



The 3-yr-olds were already quite abundant by 1 

 July and reached a peak in numbers by late July 

 (Fig. 1), suggesting that arrival was completed by 

 late July. Kenyon and Wilke (1953) similarly noted 

 the maximum number of 3-yr-olds on hauling 

 grounds was after mid-July. This age group 



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