Table 24. --Data on the mean weight of untagged pups and the 

 kill of male seals at ages 3 and 4 from the same year class 

 year classes 1957-63, St. Paul Island 



it is reasonable to assume as a first approxi- 

 mation that: 



1957 

 1958 

 1959 

 1960 

 1961 

 1962 

 1963 



8.7 

 11.4 

 9.4 

 9.8 

 8. 5 

 9.2 

 8.9 



1/ 



1/ Estimated by using the kill of 25, 535 3-year-oids in 1966 

 plus the forecast given earlier in this section of 14. 300 4- 

 year-olds that will be taken in ISo/. 



The regression equation is: 



K = 8,070W - 36,650 (r^ = 0.44 r = 0.66) 



where W = mean weight of untagged pups in 



kg. 

 K = kill on St. Paul Island at ages 3 and 

 4 from the same year class (in 

 thousands). 



As pointed out previously, the regression 

 is greatly affected by a single point--that of 

 the 1958 year class. Adjustment miust also be 

 made for the shortness of this series as com- 

 pared to most regressions used in these pre- 

 dictions. 



^ For the 1964 year class W = 9.1, and hence 

 K = 36,800. This regression implies a kill of 

 3-year-old males in 1967 of 24,700, as de- 

 rived from (36,800)(0.67). The standard error 

 of K is 10,600. 



Regression of the Percentage of Year 

 Class Taken in the Harvest on the 

 Dead-Pup Count Percentage 



This is a new method of prediction- -one 

 that uses the counts of dead pups and esti- 

 mates of the size of the pup population in 

 autumn. 



The number of pups that die during their 

 first summer is related to the eventual harvest 

 of the year class because the greater the 

 proportions dying immiediately, the fewer can 

 survive to ages 3 and 4. Furthermore, if the 

 percentage of dead pups is a reflection of the 

 condition of the year class, this percentage 

 may indirectly measure the ocean mortality 

 that occurs during the first winter at sea and 

 perhaps also in later years. More specifically. 



K 



a+b 



D 



(3) 



where K 

 D 



the kill from a year class 

 the count of dead pups, i.e., the 

 number of pups that die during 

 their first sumnner, and 

 Nq = the estimate of the number of 

 pups born. 



To obtain a usable series of data, some 

 assumptions must be made concerning the 

 number of seals born from 1950 through 

 1960. The accumulative estimates developed 

 by Chapman (1964) seem to agree closely 

 with the fall sampling estimates shown in 

 recent reports provided \ is between 1.0 and 

 1.25 (\ represents the differential ratio of 

 survival of females to males from birth to 

 3 years of age). 



Estimates of the number of pups born have 

 been derived from Chapman (1964, table 8) 

 by interpolating for \= 1.1, with some modi- 

 fications. This computation yields the number 

 of mature (age 3 and older) females which, 

 when multiplied by 0,6 (pregnancy rate of 

 mature females), provides an estimate of the 

 number of pups born. Since the first seven 

 estimates, 1950 through 1956, differed only 

 slightly--much less than expected from the 

 unaccounted for fluctuations in pregnancy rate 

 and natural mortality--it seemed preferable 

 to replace these estimates by a 7-year average 

 of 450,000 (table 25). 



Table 25. — Estimated number of pups born, count of dead 

 pups, and number of male seals killed at ages 2 to 5, 

 year classes 1950-62, St. Paul Island 



Number 



Number 



Number 



Number of pups born-coiint of aead pups 

 ■' Estimated as in Chapman (1964). 



28 



