Tabic 19- --Data for regression of the kill of 4-year-old male seals 

 on the kill of 3-year-old male seals, median date of the 

 kill of 3-year-old male seals, and starting date of the 

 kill, year classes 1952-65, St. Paul Island 



1/ Kill of 4-year-old males to 31 July plus 80 percent of the 

 kill of 3-year-old males in August of the previous year. 



thousand for the kill of 4-year-old males on 

 St. Paul Island in 1970. 



Estimate of the kill of 4-year old male 

 seals from the yearling male seal popula- 

 tion estimate. — If an accurate estimate of the 

 number of yearling males can be made and if 

 the largest and most variable component of 

 mortality occurs during the first year of life, 

 this estimate should be the best forecasting tool. 

 Whereas the estimates of yearling males from 

 the combined kill of seals from each year class 

 have seemed reasonable and consistent, the 

 estimates based on tags recovered in different 

 years for the same year class are inconsistent. 

 For example, estimates based on tag recoveries 

 from 2-year-olds have been unreasonably low. 

 Also, estimates of each year class from returns 

 of tags at successive ages (2, 3, 4, and 5) have 

 almost consistently shown an increasing trend, 

 often with very large increases. 



Two estimates of the size of the 1966 year 

 class at age 1 are available for predicting the 

 kill of 4-year-old males in 1970, one based on 

 2-year-old tag recoveries and another on re- 

 coveries at age 3. Because our estimates from 

 the latter have been closest to estimates based 



on data combined from ages 2 and 3, we have 

 used them in the following prediction: 



The estimated regression based on data in 

 table 20 is 



K 3 + 4 = 0.376Y 

 where 



K 3+4 

 Y 



kill of 3- and 4-year-old males on 

 St. Paul Island 



estimate of yearling population, 

 Pribilof Islands. 



For the 1966 year class Y = 74.0 and hence 

 K 3 +4 = 27.8 thousand. Because the kill in 

 1969 was 17.8 thousand, the estimated 4-year- 



Table 20. — Observed kill of 3- and 4-year-old male seals, 

 St. Paul Island, and estimated number of yearling 

 male seals, Pribilof Islands, Alaska, year classes 

 1961-63 and 1965 



Year 

 class 



Estimate of yearling 



male seals, 



Pribilof Islands 



Kill of 3- and 4-year- 

 old male seals 

 St. Paul Island 



22 



