FISHERY BULLETIN: VOL. 81, NO. 1 



on St. Paul Island. Gentry (footnote 4) made simi- 

 lar observations on nursing fur seals in the late 

 1970's and found no significant change in time at 

 sea from those of Bartholomew's study. 



Pup Survival to Age 2 



Lander (1981) calculated early survival rates 

 to age 2 for male fur seals from the 1950-70 year 

 classes. York and Hartley (1981) analyzed these 

 estimates, using Mann-Whitney and Student's t 

 tests, and found pre- 1956 rates to be significantly 

 lower than post-1956 rates (0.32 vs. 0.40 aver- 

 age). This does not appear to support the hypothe- 

 sis of reduced carrying capacity. 



Time Trends in Fur Seal Diets 



Fur seal stomach contents taken in 1960, 1962- 

 64, 1968, and 1973-74 cruises were used to inves- 

 tigate trends in fur seal diets to see whether these 

 might have changed after development of the 

 pollock fishery. These data were summarized by 

 month. 



Figure 5 indicates that the age composition in 

 catch in the pollock fishery shifted from a mode 

 of 4 yr in 1964 to 3 yr in 1974 with the 2-yr-old 

 catch also being strongly represented. H. Kaji- 

 mura, who was present on the cruises, suggested 

 that the size of pollock in fur seal stomach sam- 

 ples decreased from 1964 to 1974. Examination 

 of average volume per pollock specimen in fur 

 seal stomachs (Unpubl. data 16 ; Table 2) corrobo- 

 rates this observation, with average specimen 

 size decreasing significantly between 1968 and 

 1973-74. We also note that the percentage volume 

 of the total stomach content comprised of pollock 

 was consistently high in 1973-74 (>48%), while 

 earlier, especially before 1968, pollock comprised 

 a variable and usually low percentage of the diet 

 (<20% in 8 of the 11 mo sampled). 



These data indicate that there may have been 

 an interaction between fur seal diets and the pol- 

 lock fishery. As fishing pressure on pollock in- 

 creased, fishing out of older age classes reduced 

 the average size of the fish and increased the 

 average growth rate of the pollock. Furthermore, 

 young pollock survival may have been increased 

 through reduced cannibalism. These increased 



en 



a 



on 



=3 



o 



H 



z 



to 



-J 



a 



> 



a 



z 



i— i 



O 



8 



4 



O 

 6 



4 





 8 



4 



O 

 8 



4 





 8 



4 





 8 



O 

 8 



W 4 



O 

 8 



O 

 8 



4 



O 

 8 



O 

 8 



4 



O 



1964 

 CW 8.53 

 CN 15,214 



1965 

 CW 9.25 

 CN 15,462 



1966 

 CW 6.83 

 CN 12,009 



1967 

 CW 8.23 

 CN 14,764 



968 



CW I 1.84 

 CN 21,574 



1969 



CW 10.41 



CN 18,965 



19 70 

 CW 8.99 

 CN 19,453 



1971 



CW 5.79 



CN 12,392 



1972 

 CW 9.33 

 CN 20,493 



973 



CW 6.25 

 CN 16,347 



1974 

 CW 5.38 

 CN 15,51 



23456789 

 AGE 



Figure 5.— Age composition in catch per unit effort (CPUE) of 

 walleye pollock from the Japanese trawl fishery in the eastern 

 Bering Sea. Japanese trawl fishery includes the mothership 

 fishery and the North Pacific trawl fishery, but not land-based- 

 dragnet fishery. From Salveson and Alton (text footnote 12). 

 C W = CPUE in weight in metric tons; CN = CPUE in number. 



16 Data obtained from Dr. M. Tillman, Director, Northwest 

 and Alaska Fisheries Center National Marine Mammal Lab- 

 oratory, National Marine Fisheries Service, NOAA, 7600 Sand 

 Point Way NE., Seattle, WA 98115. 



stocks of smaller fish were reflected by the in- 

 crease in abundance of pollock in fur seal diets 

 after 1968 and by a marked decrease in the aver- 

 age size of fish taken by the fur seals. This in- 



128 



