BIGG: ARRIVAL OF NORTHERN FUR SEALS 



appeared to have the largest number of males 

 returning. 



4-Year-Olds 



The number of males killed of age 4 remained 

 essentially constant during July, except for a 

 decrease in late July (Fig. 1). Although no distinc- 

 tive peak in numbers was evident, several factors 

 suggest the main arrival was probably completed 

 by mid-July. First, the number killed in the first 

 round (i.e., up to 1 July) was likely to have been too 

 large relative to later rounds because of an accum- 

 ulation of males that arrived before the kill began. 

 This situation was most obvious for kills of males 

 ages 5 and 6 (Fig. 2), but also could have existed 

 to some extent for the kill of males ages 2 and 3. 

 For ages 2 and 3, the accumulation would not have 

 been as obvious because the main arrival time was 

 after kills began. Secondly, the true peak in number 

 killed of 4-yr-olds was probably flattened by the high 

 harvest utilization rate of this age. Finally, an ex- 

 amination of the trend in numbers killed by round 

 for individual years indicated the seasonal pattern 

 was quite variable, ranging between that noted for 

 males age 3, and that for males age 5. For exam- 

 ple, the arrival time for 4-yr-olds in 1971 was similar 

 to that seen for the typical 3-yr-olds; it was similar 

 for the typical 5-yr-olds in 1968; and in 1980 it was 

 intermediate, with a distinctive peak in mid-July. 

 Such variations tended to dampen the peak. Kenyon 

 and Wilke (1953) remarked that the maximum 

 number of males older than 3 yr arrived before mid- 

 July. Fewer age-4 males returned than age-3 males, 

 probably due to the large kill at age 3. 



5-Year-Olds 



Most 5-yr-olds appeared to have already arrived 



6 II 16 21 26 31 

 JULY 



5 10 15 20 

 AUGUST 



Figure 2.— Mean number, and standard error, of northern fur seal 

 males killed of age 5-6 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. 



by early July (Fig. 2). However, as noted for 4-yr- 

 olds, the kill by 1 July was probably large relative 

 to the number killed in later rounds. Most males 

 probably arrived by late June to early July, assum- 

 ing the time in peak numbers of 5-yr-olds was earlier 

 than mid-July, but not earlier than for territorial 

 bulls (>7 yr) on rookeries. Fewer 5-yr-olds returned 

 than 4-yr-olds because of the large kill of males at 

 age 4. 



6-Year-Olds 



As with 4- and 5-yr-olds, the first kill was likely 

 too large. Most 6-yr-olds probably arrived by late 

 June. Gentry (1981) tagged juvenile males on haul- 

 ing grounds of St. George Island in 1977 and count- 

 ed them during late May to mid- August 1980. Al- 

 though the ages were not known with certainty, the 

 most common age in 1977 was likely 3 yr, with a 

 range of 2-5 yr (R. Gentry 4 ), and thus most males in 

 1980 were probably 6 yr of age. His counts indicated 

 numbers began to increase in late May, reached a 

 peak on 19-28 June 1980, and declined thereafter. 



^7-Year-Olds 



No males older than 6 yr of age were taken in the 

 annual kills on hauling grounds. This was because 

 the upper length limits excluded these ages from 

 kills, and because many males of these ages go to 

 rookeries for breeding rather than to hauling 

 grounds. 



Arrival of Males on Rookeries 



1 -Year-Olds 



Behavioral studies suggest most yearling males 

 probably arrived on rookeries by late September to 

 early October, and the number returning was the 

 smallest of any age group of males. Osgood et al. 

 (1915) reported that branded male yearlings were 

 rarely seen between late July and mid- August but 

 became more numerous later, although they always 

 remained small in number. Kenyon and Wilke (1953) 

 mentioned yearlings of unspecified sex returned 

 principally in September to November, and that only 

 a few individuals were involved. Using counts of 

 tagged yearlings seen on rookeries between 17 

 September and 17 October, Roppel et al. (1965a) 



4 R. Gentry, Northwest and Alaska Fisheries Center, National 

 Marine Fisheries Service, NOAA, 7600 Sand Point Way N.E., 

 Seattle, WA 98115, pers. commun. February 1984. 



387 



