94 



U. S. BUREAU OF FISHERIES 



actual counts, that there were at least 3,000 surplus bulls on the haul- 

 ing grounds of both islands; therefore, for the present season, a 

 deduction of 50 per cent, for losses due to fighting, natural causes, 

 and errors in loss percentage in previous years, was not necessary. 

 If this deduction had been made, it would have shown only 1,646 

 surplus bulls on hand, compared with 3,943 in 1930. Obviously, this 

 would have been incorrect. 



Observations indicate that there were more than 13,198 3-year-old 

 males on hand on August 10. This would indicate a smaller mor- 

 tality rate during a portion of their previous existence or a greater pup 

 increase than 8 per cent, or a combination of both. However, no 

 change has been made in mortality rates, and no adjustment has been 

 made to take care of the apparently greater number of 3-year-olds on 

 hand than computation indicates. No change should be made until 

 it is fully evident that such increases or decreases will remain constant 

 from year to year. 



Reports of previous years show reasons for methods used in de- 

 termining mortaUty rates. 



COMPLETE COMPUTATION 



The following complete computation shows the various methods 

 used at present to determine the approximate number of seals of the 

 various age classes in the herd. It will be noted that there were 

 81,981 more animals at the end of the seahng season of 1931 than 

 were present at the same time the previous season. This is an in- 

 crease for the herd of 7.84 per cent, as compared with an increase of 

 7.57 per cent in 1930. It also compares favorably with the 8 per cent 

 increase of pups and cows. 



Complete computation of fur seals, Pribilof Islands, as of August 10, 1931 



Class 



Pups, estimated 



Breeding cows, 3 years old and over, by inference 



Harem bulls, counted ._ 



Idle bulls, counted _ , 



Yearlings, male and female, estimated: 



Females born in 1930 



Natural mortality, 40 per cent 



Yearling females, Aug. 10, 1931 



Males born in 1930 _ 



Natural mortality, 40 per cent 



Yearling males beginning 1931 



Yearling males killed in 1931 



Yearling males, Aug. 10, 1931 



2-year-olds, male and female, estimated: 



Yearling females, Aug. 10, 1930 



Natural mortality, 15 per cent 



2-year-old females, Aug. 10, 1931 



Yearling males, Aug. 10, 1930 



Natural mortality, 17.5 per cent 



2-year-olds beginning 1931 



2-year-olds l<illed in 1931 



2-year-oId males, Aug. 10, 1931 



St. Paul 

 Island 



292, 569 



292, 569 



7,557 



1,519 



135, 453 

 54, 181 



81, 272 



135, 452 

 54, 181 



81,271 

 12 



81, 259 



75, 253 

 11,288 



63,965 



75, 238 

 13, 167 



62, 071 

 1.064 



61, 007 



St. George 

 Island 



66, 073 



66,073 



1,676 



369 



30, 590 

 12, 236 



18, 354 



30,589 

 12, 236 



18, 353 



18, 353 



16, 994 

 2,549 



14, 445 



16, 994 

 2,974 



14, 020 

 199 



13, 821 



Total 



358, 642 



358, 642 



9,233 



1,888 



166, 043 

 66, 417 



166, 041 

 66, 417 



99, 624 

 12 



99, 612 



92, 247 

 13, 837 



78, 410 



92, 232 

 16, 141 



76, 091 

 1,263 



74, 828 



