FISHERY BULLETIN: VOL. 81. NO. 3 



molluscs dominate the benthic biomass. The separa- 

 tion of the feeding grounds of gray whales and walrus 

 can be documented by side-scan sonar, which clearly 

 relates general changes in surface sedimentary struc- 

 tures to the large-scale feeding activities of gray 

 whales and walrus. 3 When properly calibrated with in 

 situ observations, individual feeding excavations and 

 multiple excavation patterns (footnote 2) may be 

 accurately interpreted on side-scan sonographs 

 (pers. obs. by authors). 



Gray whales also produce benthic feeding ex- 

 cavations along Vancouver Island in British Colum- 

 bia (footnotes 3, 4). Fecal material has been collect- 

 ed along this coast as well. 5 We recently discovered 

 dense beds of ampeliscid amphipods and an exten- 

 sive benthic feeding record of gray whales near the 

 Bamfield Marine Station (see footnote 2). Many 

 whales apparently feed along Vancouver Island 

 during the northward migration, and some individ- 

 uals spend the entire summer here (Darling 1977). 



In summary, despite considerable evidence of 

 benthic feeding in northern habitats, there is no com- 

 pelling evidence for benthic feeding in or near the 

 lagoons of Baja California. The southern lagoons 

 contain highly dynamic, coarse sediment harboring 

 very small infauna and little prey biomass for gray 

 whales. Most infauna are much smaller than the 

 spaces between the gray whale baleen. The structure 

 of benthic communities within the calving lagoons is 

 not influenced by gray whale activities, because bot- 

 tom communities in adjacent noncalving lagoons are 

 similar to those in the calving lagoons. 



Earlier studies of the gray whale diet imply highly 

 selective feeding on large crustaceans (e.g., Pike 

 1962). While two species of large amphipods, Pon- 

 toporeia femorata and A. macrocephala, generally ac- 

 count for much of the prey biomass (Table 2), careful 

 examination of the prey remains in a fecal slick 

 revealed a surprisingly large number of smaller prey. 

 Gray whales probably are relatively nonselective 

 filter feeders, consuming most of the large and small 

 infaunal forms. Despite the importance of benthic 

 prey, gray whales are clearly opportunistic feeders, 

 consuming both large and small benthic inverte- 

 brates, epifaunal invertebrates in kelp forests 

 (Wellington and Andersen 1978) and along rocky 



'Hans Nelson and Kirk Johnson, U.S. Geological Survey, Menlo 

 Park, CA 94025, pers. commun. August 1982. 



'J. Hudnall showed underwater slides and a movie of feeding ex- 

 cavations and behavior at the 4th Biennial Conference on the Biol- 

 ogy of Marine Mammals, San Francisco, Calif., December 14-18, 

 1981. 



M. Darling reported, at the 4th Biennial Conference on the Biology 

 of Marine Mammals in San Francisco, Calif., December 14-18,1981, 

 that K. Norris and students collected this sample nearthe Bamfield 

 Marine Station, British Columbia. 



shores (see footnote 2), zooplankton (Rice and Wol- 

 man 1971; Norris et al. in press), and fish (Gilmore 

 1961; Sund 1975). 



Although some observations of apparent feeding 

 behavior in the breeding lagoons undoubtedly in- 

 volve planktonic feeding (Norris et al. in press), and 

 opportunistic consumption of some benthic animals, 

 much of this behavior probably results in little or no 

 food. A number of other explanations are likely. For 

 example, a local fisherman and naturalist, Mario 

 Rueda, directed us to a specific habitat near Piedras 

 Island in Ojo de Liebre, where apparent feeding 

 behavior was consistently observed. This area con- 

 tained no concentrations of potential infaunal or 

 epifaunal prey. However, the bottom relief was spec- 

 tacular. Rocky outcrops formed a series of parallel 

 ridges much like giant and stable ripple marks on the 

 bottom. The vertical relief was 2 to 3 m. Between the 

 rocky crests, there were deep basins where water 

 currents were very low. The distance between crests 

 was 5 to 10 m. The tidal currents above these ridges 

 were extremely strong. Perhaps gray whales are at- 

 tracted to this current regime where individuals can 

 rapidly swim in and out of mild and strong currents 

 over an undulating bottom. 



Laguna San Quintin contains a unique bottom com- 

 munity, which is strikingly different from the lagoons 

 of California and the five lagoons that were surveyed 

 in central and southern Baja California. San Quintin 

 harbors a large number of potential gray whale prey 

 in a relatively small area. Future expansions of the 

 gray whale population may bring more whales to San 

 Quintin. If the whales arrive and do not avoid the 

 lagoon because of human activities, we predict a 

 dramatic change in the bottom communities of San 

 Quintin. A small group of whales might spend much 

 of the winter and spring feeding in San Quintin. Like 

 the relatively small feeding areas along the coast of 

 British Columbia, San Quintin could become a 

 regular stopping place for certain individuals. There 

 may be equally suitable areas for feeding around the 

 Gulf of California, where gray whales were known to 

 breed in the past (Gilmore et al. 1967). While these 

 local patches of prey may be unimportant to the en- 

 tire population, they may become important to cer- 

 tain individuals. Relatively few feeding gray whales 

 could have considerable effects on local benthic 

 habitats, and could produce long-term patterns of 

 bottom population and community change. 



ACKNOWLEDGMENTS 



We are very grateful for the considerable support of 

 Lloyd Lowry, Robert Nelson, and Kathy Frost (Alas- 



520 



