use in 1961 of body weight rather than length 

 as the criterion of age. Although preferable 

 over body weight, body length, as now used, 

 is apparently not an accurate guide for select- 

 ing yearling females. Among known-age 

 yearlings handled in 3 years, males have 

 out-numbered females by an average of over 

 4 to 1 while among seals selected as yearlings 

 the ratio was about 2 to 1 . This means that 

 over one-third of the selected females were 

 actually older than yearlings. Only a reduc- 

 tion in the maximum length limit for females 

 will reduce the error caused by the overlap 

 in body lengths of yearlings and 2-year-old 

 females. 



Survey- -Yearlings 



There is no known way to predict accurately 

 the number of 3-year-old seals that will re- 

 turn to the Pribilof Islands each year. In 

 recent years, the return has varied from 

 nearly 50,000 from the 1953 year class to 

 less than 13,000 from the 1956 year class. 

 If the assumption that each age class suffers 

 its greatest mortality during its first winter 

 at sea is correct, the relative abundance on 

 land each fall of yearlings tagged as pups 

 may provide an index to survival from birth 

 to age 1. Thus, a means of roughly predicting 

 the return of 3-year-olds will be available. 

 As a beginning to this approach, five weekly 

 counts of tagged yearlings were made on St. 

 Paul Island in 1963. 



Methods .-- Two to three men walked slowly 

 in a line perpendicular to the water's edge, 

 forcing seals from the rookery or hauling 

 ground to move toward the sea within sight of 

 two or three observers. The observers cap- 

 tured each tagged yearling seen, recorded the 

 tag number and sex, then released the animal. 

 Descriptions of rookery and hauling ground 

 sampling areas used for the surveys are given 

 in table 19. The first survey, made prior to 

 the selection of sampling areas, required 

 nearly 2 days to complete; each of four sub- 

 sequent surveys made required about 7 hours. 



Results . --The tagged yearlings found on 

 each area are listed in table 20 by date and 

 sex. Yearlings were apparently most abundant 

 during 27 September to 1 1 October. Of the 73 

 tagged yearlings captured, 65 were males and 

 8 were females. This preponderance of eight 

 males to one female is greater than the average 

 of four males to one female found among 

 tagged yearlings captured during tagging in 

 1961, 1962, and 1963. 



The mean number of tagged yearlings caught 

 per hour increased from 0.80 in 1961 to 3.06 

 in 1962; the ratio in 1963 was 2.33 per hour. 

 A similar comparison results even if other 

 than total periods are used. Using 27 Septem- 

 ber through 11 October, for instance, the 



Table 19. — Description of rookery and hauling 

 ground sampling areas surveyed for tagged 

 yearling counts, St. Paul Island, 1963 



NEP through REEF were surveyed in the 

 morning; T0L through ZAP were surveyed in 

 the afternoon. 



mean values for the years 1961, 1962, and 



1963 were 1.00, 3.34, and 2.87, respectively. 



Discussion .- -About the same number of 

 tagged yearlings were counted each week from 

 27 September to 1 1 October. The reduced num- 

 ber of yearlings found on 17 October agreed 

 with the observation that few seals were using 

 the hauling grounds after 15 October. Seals 

 were numerous on the rookeries, however. 



Use of specific areas for each survey tended 

 to equalize the number of seals handled in 

 each drive and permitted a survey of all areas 

 in 1 day. Surveys were postponed during bad 

 weather because many seals remain in the sea 

 during periods of heavy rainfall. 



Yearlings and 3-year-old seals are tagged 

 on the same flipper; however, 3-year-old 

 seals have a different checkmark and tag 

 series and are usually larger than yearlings. 

 When necessary, the checkmark can be used 

 to identify small 3-year-old seals without 

 capturing them. 



The survey crew must be supervised to 

 ensure that the data on age, sex, and abundance 

 of yearlings are accurately determined and 

 recorded. In addition, yearling surveys must 

 be coordinated with other activities on the 

 rookeries so that the seals are not disturbed 

 for at least 1 day before a survey. 



A series of surveys similar to those in 1963 

 should be made in 1964 to establish more 

 clearly the best period for surveying tagged 

 yearlings. Comparable results in 1963 and 



1964 would suggest that three counts from 

 27 September to 11 October would be satis- 

 factory. 



Tag loss and the proportional return of 

 yearlings to land must be constant from year 

 to year if the counts are to provide a satis- 

 factory index to the survival of an age class 



18 



