OLIVER ET AL.: GRAY WHALE FEEDING GROUNDS 



(Gorsline and Stewart 1962) and Ojo de Liebre 

 (Phleger and Ewing 1962) were observed in earlier 

 studies. The Bering Sea areas, like San Quintin, con- 

 tained less mobile fine sands (Nelson 1982) harbor- 

 ing many relatively large infauna in tubes and burrows 

 (Stoker 1978). 



DISCUSSION 



The absence of fecal material, benthic feeding ex- 

 cavations, and significant quantities of potential gray 

 whale prey suggest that gray whale feeding on 

 benthic invertebrates is not common in Baja Califor- 

 nia. No evidence of benthic feeding was encountered 

 within the calving and noncalving lagoons, at lagoon 

 entrances, and along the offshore sand bottoms. Gray 

 whale stomachs collected in the southern lagoons 

 also contained no benthic prey (Scammon 1874; Rice 

 andWolman 1971). 



In contrast to Baja California, there is considerable 

 evidence of gray whale feeding in the northern Bering 

 Sea. Stomach contents are dominated by benthic in- 

 fauna, especially a few species of large amphipod 

 crustaceans (Table 2). Crustacean communities are 

 well developed in the central and western portion of 

 the area (Neiman 1963; Stoker 1978), the major gray 

 whale feeding grounds. The Russian literature 

 reports a benthic biomass of almost 1,000 g/m 2 in the 

 feeding grounds (Neiman 1963; Alton 1974), and 

 Stoker (1978) found a range from 149 to 991 g/m 2 . 

 Over 90% of the biomass was crustaceans, especially 

 A. macrocephala in the central basin. Although we on- 

 ly located a few fecal slicks in the Bering Sea, benthic 

 feeding excavations were common. 



All the large benthic excavations observed in this 

 study were undoubtedly created by feeding gray 

 whales. Other likely explanations for their origin can 

 be excluded. There are few bottom-feeding fish such 



as rays or skates in the northern Bering Sea (Shmidt 

 1950; Wilimovsky 1974). These fish produce large 

 pits in other habitats (Howard et al. 1977; Gregory et 

 al. 1979; VanBlaricom 1982). The abundant bottom 

 fish are in the cottid family (Wilimovsky 1974) and 

 are relatively nondestructive bottom feeders (pers. 

 obs.). One other bottom-feeding marine mammal, the 

 walrus, occurs in the gray whale feeding grounds, but 

 walrus produce entirely different bottom ex- 

 cavations than gray whales (Oliver et al. 2 ). We know 

 of no other likely biological explanation for the large 

 pits. 



Two physical processes produce large excavations 

 on the sea floor, ice gouging and biogenic gas crater- 

 ing. Although ice gouging produces deep excavations 

 in the sea floor (Reimnitz et al. 1977), this scour does 

 not produce regular, bowl-shaped depressions and 

 usually causes much more extensive bottom distur- 

 bance (Reimnitz etal. 1977; Larsen etal. 1981; Thor 

 and Nelson 1981; pers. obs. by authors). Release of 

 biogenic gas from the sediment apparently produces 

 large craters in Norton Sound, and several other 

 areas with gas-producing strata, but not in the gray 

 whale feeding grounds (Nelson et al. 1979). 



Gray whale feeding excavations can be easily dis- 

 tinguished from the benthic feeding record of walrus 

 (Oliver et al. 1983). Walrus excavations were com- 

 mon along the eastern shore, and gray whale ex- 

 cavations only occurred in the central study area (Fig. 

 2). Here, the gray whale prey (Stoker 1978) and feed- 

 ing gray whales (Moore and Ljungblad in press) are 

 much more abundant. Gray whales are infrequently 

 encountered along the eastern shore, where bivalve 



'Oliver, J. S., P. N. Slattery, M. A. Silbertstein, and E. F. O'Connor, 

 1983. Gray whale feeding on dense ampeliscid amphipod com- 

 munities near Bamfield, British Columbia. Unpubl. manuscr. 

 Moss Landing Marine Laboratories, Moss Landing, CA 

 95039. 



TABLE 2. — Dominant prey species contained in gray whale stomachs. All are benthic and all 

 but Synidotea sp. are amphipods. Stomachs usually contain one prey species which com- 

 prises 80 to 100% of total contents (Zimushko and Lenskaya 1970; Bogoslovskaya, et al. 

 1981). 



1 Dominant species where number of stomachs examined were unreported. 



2 Coyle, K. 0. 1 981 . The oceanographtc results of the cooperative Soviet-American cruise to tne Lhukchi 

 East Siberian Seas aboard the Soviet whale hunting ship Razyashchn, Sept. -Oct. 1 980 Unpubl. manuscr. Urn 

 sity of Alaska. Institute of Marine Science. Fairbanks, AK 99701 . 



mencan cruise to the Chukchi and 

 iver- 



519 



