considerably larger (x = 15.9 cm) (Smith 1981). The 

 corresponding average individual weights can be 

 estimated as 9.5 and 23.7 g, giving an estimated 

 biomass of age 1 pollock about 10 times greater in 

 1974 than in 1976. Therefore, the total food available 

 to predators that specialize on small pollock can vary 

 markedly, as can the energy obtained from each fish 

 consumed. Lengths and population sizes of older 

 pollock also vary somewhat among years (Smith 

 1981); however, predators feeding on large pollock 

 will undoubtedly be exploiting several age classes. 



Three species of marine mammals— harbor seals, 

 sea lions, and fur seals— consume age classes of 

 pollock that are also exploited by the commercial 

 fishery (Table 3). A major effect of the pollock fishery 

 has been a reduction in the abundance of older, 

 larger individuals (Pereyra et al. 8 ). Major declines in 

 abundance of sea lions and fur seals in the eastern 

 Bering Sea have been reported since the 1950's 

 (Braham et al. 1980; Fowler 1982). Although the 

 evidence is equivocal, especially for the fur seal (see 

 Swartzman and Haar 1983), reduced food availability 

 due to expansion of the pollock fishery has been sug- 

 gested as a possible cause of the decline in popula- 

 tions. The present population status of other pollock- 

 eating marine mammals in the Bering Sea is not 

 known. 



The sizes of fishes consumed by marine mammals 

 are obviously very important for determining the 

 nature and magnitude of marine mammal-fishery 

 interactions. It is particularly important to recognize 

 that because of different feeding strategies, changes 



8 Pereyra, W. T., J. E. Reeves, and R. G. Bakkala. 1976. Demer- 

 sal fish and shellfish resources of the eastern Bering Sea in the 

 baseline year 1976. Processed Rep., 619 p. Northwest and Alaska 

 Fisheries Center, NMFS, NOAA, Seattle, WA. 



Table 3.— Age-class distribution of walleye pollock con- 

 sumed by marine mammals in the Bering Sea, and caught 

 in the commercial fishery in 1978, based on length-at-age 

 data from Smith (1981). 



Percent of fishes in age class 

 Predator species 1 23456789 >10 



Harbor seal 43 20 23 3 3 3 6 



Spotted seal 100 — 



Ribbon seal 98 1 1 — 



Steller sea lion 21 40 14 3 5 6 4 2 2 3 



Fur seal 1 49 44 7 — 



Minke whale 100 — — — — 



Commercial 

 fishery 2 2 20 40 18 20 (>5 yr old) 



1 from McAlister et al. 1976. 

 2 from Smith 1981. 



in fish stock characteristics caused by fishing may 

 benefit some marine mammal species while having 

 no effect or being detrimental to others. 



Acknowledgments 



Support for this study was provided by the U.S. 

 Bureau of Land Management Outer Continental 

 Shelf Environmental Assessment Program and the 

 Federal Aid in Wildlife Restoration Program. Num- 

 erous colleagues, particularly John J. Burns and 

 Larry M. Shults, assisted in the collection and 

 processing of specimens. We are particularly grateful 

 to Donald G. Calkins, Thomas R. Loughlin, and 

 George Antonelis for providing us unpublished in- 

 formation. Graphics and statistical analyses were 

 done by Jesse Venable Clifford H. Fiscus made help- 

 ful comments on an earlier draft of the manuscript. 

 We also thank two anonymous reviewers whose com- 

 ments substantially improved the manuscript. 



Literature Cited 



Bakkala, R., K. King, and W. Hirschberger. 



1981. Commercial use and management of demersal fish. In 

 D. W. Hood and J. A. Calder (editors), The eastern Bering 

 Sea shelf: oceanography and resources, Vol. 2, p. 1015-1036. 

 U.S. Dep. Commer., Off. Mar. Pollut. Assessment, NOAA, 

 Rockville, MD. 



Braham, H. W., R. D. Everitt, and D. J. Rugh. 



1980. Northern sea lion population decline in the eastern 

 Aleutian Islands. J. Wild]. Manage 44:25-33. 



Bukhtiyarov, Y. A., K. J. Frost, and L. F. Lowry. 



1984. New information on foods of the spotted seal, Phoca 



largha, in the Bering Sea in spring. In F. H. Fay and G. A. 



Fedoseev (editors), Soviet-American cooperative research on 



marine mammals, Vol. 1 - Pinnipeds, p. 55-59. U.S. Dep. 



Commer., NOAA Tech. Rep. NMFS 12. 

 Fiscus, C. H., G. A. Baines, and F. Wilke. 



1964. Pelagic fur seal investigations, Alaska waters, 1962. 



U.S. Fish Wildl. Serv., Spec Sci. Rep. Fish. 475, 59 p. 

 Fowler, C. W. 



1982. Interactions of northern fur seals and commercial fish- 

 eries. Trans. N. Am. Wildl. Nat. Resour. Conf. 47:278-292. 



Frost, K. J. 



1981. Descriptive key to the otoliths of gadid fishes of the Ber- 

 ing, Chukchi, and Beaufort Seas. Arctic 34:55-59. 



Frost, K. J., and L. F. Lowry. 



1980. Feeding of ribbon seals (Phoca fasciata) in the Bering 

 Sea in spring. Can. J. Zool. 58:1601-1607. 



1981a. Trophic importance of some marine gadids in north- 

 ern Alaska and their body-otolith size relationships. Fish. 

 Bull., U.S. 79:187-192. 



1981b. Foods and trophic relationships of cetaceans in the Ber- 

 ing Sea. In D. W. Hood and J. A. Calder (editors), The 

 eastern Bering Sea shelf: oceanography and resources, Vol. 

 2, p. 825-836. U.S. Dep. Commer., Off. Mar. Pollut. Assess- 

 ment, NOAA, Rockville, MD. 



1981c Ringed, Baikal, and Caspian Seals. In S. H. Ridgway 

 and R. J. Harrison (editors), Handbook of marine mammals, 

 Vol. 2, Seals, p. 29-53. Acad. Press, N.Y. 



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