SWARTZMAN and HAAR: INTERACTIONS BETWEEN FUR SEALS AND FISHERIES 



that the available data from which these indices 

 are computed be also studied for trends. Indices 

 that are most easily obtained for the fur seal are 

 pup birth estimates, dead pup counts, male sur- 

 vival to age 3 (from male harvest data), and 

 length at age for preadult males (from harvested 

 males). 



Fur Seal Diet Trend 



We have suggested a relationship between fur 

 seals and the fishery via greatly increased abun- 

 dance of juvenile pollock (Table 2). The data 

 used, however, were already combined in such a 

 way that we were unable to separate the data by 

 region where the data were collected and the de- 

 gree of digestion of the prey. We suggest that the 

 original data be used to conduct a complete sta- 

 tistical analysis with corrections made for the 

 area in which the sample was taken and, if pos- 

 sible, the time of day the samples were taken 

 (assuming that the correlations found between 

 the proportion of the stomachs empty and time of 

 day the samples were taken also applies to the 

 percentage of food digested). Variance estimates 

 can also be computed and used to make statisti- 

 cal tests for time trends both in the average size 

 of pollock in fur seal stomachs and in the percent- 

 age of the total diet comprised of pollock. 



Role of Patchiness in Seal Feeding 



Although we suspect from survey data on pol- 

 lock (Smith 1979) that pollock are quite patchily 

 distributed in the eastern Bering Sea, the survey 

 data need to be reexamined for an indication of 

 the size of patches or degree of aggregation. An . 

 attempt should be made to represent this patchi- 

 ness stochastically (in terms of probability). One 

 important question to be considered with these 

 data is whether or not there has been a trend in 

 pollock school size from 1963 to 1974 in the east- 

 ern Bering Sea. Another approach to consider 

 patchiness is to use the abundance of pollock in 

 fur seal stomachs collected at different locations 

 as an index to the spatial separation and size of 

 pollock schools. 



Suggested Future Data Collection 



We suggest that a fish trawl survey targeting 

 on pollock be conducted between the Pribilof 

 Islands and Unimak Pass from June to Septem- 

 ber with study designed to focus on areas of high 



pollock density to determine the size distribution 

 of pollock, the size of the schools, and, if possible, 

 to observe fur seal feeding intensity around 

 the schools. The pollock and fur seals might be 

 tracked by using multibeam sonar techniques. 

 Additional stomach samples of fur seal taken in 

 conjunction with the trawl survey would give 

 useful insight into fur seal food selectivity. 



CONCLUSIONS 



In summary, we see rookery fur seal behavior 

 and multispecies, age-classed, patch-feeding 

 models as directions for future study. Before pro- 

 ceeding in this direction we recommend further 

 detailed analyses of the fur seal stomach content 

 data, to explore more fully the interaction be- 

 tween the fur seal and the walleye pollock fishery 

 (Table 2), and to elucidate other interactions 

 with fisheries of which we may be unaware at 

 this time. 



The available fur seal and fishery data, while 

 limited, appear to be the best mammal-fishery 

 data in the world and as such deserve to be fully 

 archived and fully utilized. 



ACKNOWLEDGMENTS 



The authors wish to acknowledge the help of 

 Anne York, Jerry Hornof, Mike Perez, Hiro 

 Kajimura, Bruce McAlister, Ron Ryel, Jim Ber- 

 dine, and Mike Tillman in conducting the work 

 which led to this report. We are especially grate- 

 ful to Chuck Fowler for his ideas, support, and 

 his making data and other resources openly avail- 

 able to us. 



Others whom we appreciate for help in review- 

 ing the manuscript and/or providing suggestions 

 on our work include Gary Smith, Robert Francis, 

 and Taivo Laevastu at NWAFC; Nigel Bonner of 

 Cambridge, England; Douglas Chapman at the 

 University of Washington; Robert Hofman and 

 Peter Major of the Marine Mammal Commis- 

 sion; and Lee Eberhardt at Battelle Pacific 

 Northwest Laboratory. In our office Ed Small 

 and Stan Clark supplied computer support and 

 Pat Sullivan editorial and clerical assistance. 



This work was funded in part by the Marine 

 Mammal Commission. 



LITERATURE CITED 



Abegglen, C. E., AND A. Y. Roppel. 



1959. Fertility in the northern fur seal, 1956-57. J. 



131 



