OLIVER ET AL.: WALRUS FEEDING IN BERING SEA 



benthic feeding records in areas where the species do 

 and do not overlap. 



Walrus and sea otters may compete for food in the 

 southeastern Bering Sea, where sea otters forage ex- 

 tensively in soft-sediment habitats. In contrast to the 

 situation in rocky shores (e.g., Estes et al. 1982), the 

 feeding ecology of sea otters in soft sediments is 

 poorly understood. Along the California coast, sea ot- 

 ters feed on several species of bivalves, including Pis- 

 mo clams, Tivela stultorum; Washington clams, 

 Saxidomus nuttallii; and gaper clams, Tresus nuttallii 

 (Stephenson 1977; Hines and Loughlin 1980), on 

 tellinid clams Tellina sp. in Prince William Sound (G. 

 A. VanBlaricom 5 ), and on razor, Siliqua alta, and 

 surf, Spisula polynma, clams along the Alaska Penin- 

 sula (pers. obs.). They excavate pits with the fore limbs 

 and commonly produce sediment piles next to the ex- 

 cavation. Unlike the sea otter, walrus pits do not have 

 piles of extracted sediment. Because otters break 

 shells to extract soft parts, the discarded shells of 

 walrus and sea otters are easily separated as well. 

 Walrus feed along the northeastern portion of the 

 Alaska Peninsula, 6 while sea otters occur more to the 

 southwest. However, their ranges do overlap in the 

 central area. Therefore, feeding records can be quan- 

 tified in areas of overlap and non-overlap for both 

 species. 



Walrus and bearded seals may compete for bivalves 

 in the northern Bering and Chukchi Seas (Lowry et al. 

 1980). Although we have not observed the benthic 

 feeding record of bearded seals, we predict that it is 

 distinct from the walrus record, and thus amenable to 

 the same sampling scheme outlined for the sea otter- 

 walrus feeding grounds in the southern Bering Sea. 



Gray whales do not consume large bivalves, but they 

 may have a negative effect on the walrus food re- 

 source by reducing the recruitment or survival of 

 walrus prey. One possible hypothesis is that gray 

 whale feeding kills clams by direct burial, or by clog- 

 ging feeding structures. We predict that this hy- 

 pothesis is incorrect. A more likely hypothesis is that 

 gray whale disturbance has a positive influence on 

 several species of amphipod crustaceans, and that 

 these crustaceans decrease the recruitment of young 

 bivalves by predation, trampling, or some less direct 

 interference. This idea can be tested by excluding 

 whales from a bottom area with a large (perhaps 20 X 

 20 m) canopy made of net on a pipe frame. Walrus 



5 G. R. VanBlaricom, U.S. Fish and Wildlife Service, Piedras Blan- 

 cas Field Station, P.O. Box 67, San Simeon, CA 93452, pers. com- 

 mun. December 1981. 



"Fay, F. H., and F. L. Lowry. 1981. Seasonal use and feeding 

 habits of walruses in the proposed Bristol Bay clam fishery area. 

 North Pac. Fish. Manage. Counc, Doc. 18, 60 p. 



feeding probably has little or no effect on gray 

 whales. 



This discussion speculates broadly about the use- 

 fulness of the benthic feeding record. But much of the 

 speculation can be formulated into hypotheses that 

 are subject to critical tests. Comparable ideas about 

 most other marine mammals, especially the non- 

 bottom-feeding species, are extremely difficult to 

 test, either by manipulative experiments or by sam- 

 pling natural contrasts. For this reason, the benthic 

 feeding record will undoubtedly make important 

 contributions to our understanding of foraging be- 

 havior, community roles, and interactions among 

 marine mammals. 



ACKNOWLEDGMENTS 



We are deeply grateful to our co-worker, Robert 

 Nelson, and the entire group at the Alaska Depart- 

 ment of Fish and Game in Nome. The department 

 provided essential logistic support. Robert Nelson, 

 Mark Silberstein, and Allan Fukuyama helped in all 

 aspects of this study. Bud Fay, Kathy Frost, Allan 

 Fukuyama, Robert Nelson, Mark Silberstein, and 

 Glenn VanBlaricom improved the presentation and 

 our understanding of bottom-feeding mammals. 

 Lynn McMasters illustrated the figures, and Rosie 

 Stelow typed the manuscript. The work was gen- 

 erously supported by the World Wildlife Fund, the 

 American Cetacean Society, and later by the Na- 

 tional Science Foundation (DPP 8121722). 



LITERATURE CITED 



Anonymous. 



1978. Mammals in the Seas. Report of the FAO advisory 

 committee on marine resources research working party on 

 marine mammals. FAO Fish. Ser. 5:1-275. 

 DUGGINS, D. 



1980. Kelp beds and sea otters: an experimental ap- 

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 ESTES, J. A., AND J. F. PALMISANO. 



1974. Sea otters: Their role in structuring nearshore com- 

 munities. Science 185:1058-1060. 



Estes, J. A., N. S. Smith, and J. F. Palmisano. 



1978. Sea otter predation and community organization in the 

 western Aleutian Islands, Alaska. Ecology 59:822-833. 

 Estes, J. A., R. J. Jameson, and E. B. Rhode. 



1982. Activity and prey selection in the sea otter: influence of 

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 Dayton, P. K. 



1975. Experimental studies of algal canopy interactions in a 

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Fay, F. H. 



1982. Ecology and biology of the Pacific walrus, Odobenus 



511 



