unreasonably low compared to estimates from 

 recoveries at ages 3 and 4. If the source of this 

 bias was known, perhaps we could determine 

 whether it is additive or multiplicative, and 

 hence correct for it, or determine that it is 

 variable and cannot be corrected. Without a 

 complete understanding of the situation, we 

 must proceed empirically. Thus, a reliable 

 estimate through this method will be achieved, 

 if at all, only after several more years of data 

 are available. 



FORECAST OF THE KILL OF 4-YEAR OLD 

 MALE SEALS ON ST. PAUL ISLAND 



Four methods currently used to forecastthe 

 kill of 4-year-old males are: (1) Regression 

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

 3-year-old males and the mean round of the 



Mean round = mean of rounds weighted by number 

 taken by round. See glossary. 



kill of 3-year-old males; (2) regression of 

 returns at ages 3 and 4 on mean air tempera- 

 ture and on weights of live pups in autumn; (3) 

 regression of the kill on the count of dead pups 

 and the estimate of the pup population; and (4) 

 estimate of returns based on estimates of the 

 yearling population. 



Regression of the Kill of 4 -Year -Old Male 

 Seals on the Kill of 3 -Year -Old Male Seals 

 and the Mean Round of the Kill of 3 -Year -Old 

 Male Seals 



In this regression the data from the 1953 and 

 subsequent year classes are used, with 5 

 August considered the terminal date for the 

 male kill and with adjustments made where 

 necessary. Table 19 shows the data. 



The resulting regression is: 



Y=0.375X 1 + 14.19X 2 -48.31 



Table 19. — Data for regression of the kill of 4-year-old male seals 

 based on the kill of 3-year-old male seals and mean round of the 

 kill of 3-year-old male seals, year classes 1953-63, St. Paul 

 Island 



1/ The mean round of the kill of 3 -year -old males through 

 5 August; kills before 7 July were pooled into the round of 7-11 July, 

 and this period was considered as round 1. 



2/ The kill of 4-year-old males before 5 August adjusted 

 according to termination of the kill of 3-year-old males the previous 

 year. If killing ended after 5 August, this figure was increased by 

 80 percent of the number of 3-year-old males taken after 5 August. 

 If killing ended before 5 August, this figure was decreased by 80 

 percent of the estimated number of 3-year-old males that could have 

 been taken from the actual termination date through 5 August. 



3/ The killing of males in 1958 ended 31 July; an estimated 

 4,000 3-year-old males could have been taken 1-5 August. 



4/ The killing of males in 1959 ended 31 July; an estimated 

 1,500 3-year-old males could have been killed 1-5 August. 



19 



