A COMPARISON OF GRAY WHALE, ESCHRICHTIUS ROBUSTUS, 

 FEEDING IN THE BERING SEA AND BAJA CALIFORNIA 



John S. Oliver, Peter N. Slattery, Mark A. Silberstein, and Edmund F. O'Connor' 



ABSTRACT 



Our observations indicate that gray whale feeding on benthic invertebrates is rare in the calving lagoons of 

 Baja California and along the open coast near the Scammon's Lagoon complex. The biomass of benthic inver- 

 tebrate prey is 20 times greater in the northern feeding grounds of the Bering Sea (482 vs. 24 g/m 2 ). Although 

 the abundance of infaunal invertebrates is only 1.5 times greater in the Bering Sea, most infauna in the calv- 

 ing lagoons are very small polychaetes, bivalves, and crustaceans inhabiting dynamic, coarse sands. The low 

 infaunal abundance and biomass are not caused by gray whale activities in the calving lagoons, as adjacent 

 southern lagoons which are rarely utilized by gray whales have the same infaunal patterns. San Quintin has a 

 unique bottom community which is strikingly different from the more southerly lagoons in Baja California, as 

 well as the northern lagoons in California. Surprisingly, San Quintin shares a number of faunal similarities 

 with gray whale feeding areas in the Bering Sea. No fecal material or bottom excavations made by feeding 

 whales were found in the lagoons of Baja California, including San Quintin. However, the possible expansion 

 of the gray whale population may lead to dramatic changes in the rich bottom communities of San Quintin, 

 and perhaps in shallow water benthic assemblages along the migration route, and in the Gulf of California, 

 which also may harbor potential infaunal prey of gray whales. 



Gray whales, Eschrichtius robustus, are the only 

 baleen whales that feed primarily on benthic inver- 

 tebrates (Pike 1962; Rice and Wolman 1971). They 

 consume large numbers of benthic infauna, especial- 

 ly amphipod crustaceans (Zimushko and Ivashin 

 1980), apparently by ingesting sediment and filtering 

 the infauna on the baleen while expelling sediment 

 and other particles that pass through the baleen 

 fringes (Ray and Schevill 1974). The major feeding 

 grounds are the northern Bering Sea, particularly the 

 central and western regions, and the Chukchi Sea 

 (Bogoslovskaya et al. 1981). Here, the water depths 

 are generally 30 to 40 m and the extensive and 

 shallow continental shelf, the Beringian Platform, 

 supports the largest numbers of bottom-feeding 

 marine mammals in the world. In addition to gray 

 whales, walruses, bearded seals, and sea otters feed 

 primarily on benthic invertebrates in the Bering and 

 Chukchi Seas (Lowry and Frost 1981; Frost and 

 Lowry 1981). 

 Most gray whales leave the northern feeding 

 grounds in the fall and migrate over 10,000 km to Ba- 

 ja California, where calving occurs in several large, 

 shallow, protected lagoons (Scammon 1874). The 

 whales return to the Bering Sea as the sea ice 

 degenerates in the late spring (Rice and Wolman 

 197 1). Very little feeding is believed to occur outside 





'Moss Landing Marine Laboratories, Moss Landing, CA 95039. 



Manuscript accepted December 1982. 

 FISHERY BULLETIN: VOL. 81. NO. 3. 1983 



the northern feeding grounds, as gray whale 

 stomachs are generally empty along the migration 

 route (Scammon 1874; Andrews 1914; Pike 1962; 

 Rice and Wolman 1971), and in the southern lagoons 

 (Scammon 1874). However, feeding has been suggest- 

 ed (Gilmore 1961; Pike 1962; Sund 1974) or 

 documented (Howell and Huey 1930; Mizue 1951; 

 RiceandWolman 1971) outside the northern feeding 

 grounds on several occasions. 



There is additional evidence that gray whale feed- 

 ing may be relatively common in and near the calving 

 lagoons (Norris et al. in press). In the Bering Sea, 

 many naturalists have observed distinct sediment 

 plumes behind whales that apparently were filtering 

 benthic invertebrates from ingested bottom 

 sediments (Wilke and Fiscus 1961; Pike 1962; 

 Harrison 1979; pers. obs. by authors). Similar sedi- 

 ment plumes or trails have been observed in the calv- 

 ing lagoons (Walker 1975; Norris etal. 1977; Sprague 

 et al. 1978; Norris et al. in press), as well as sediment- 

 laden water passing through the baleen (Norris et al. 

 in press). This behavior suggests benthic feeding 

 similar to that observed in the Bering Sea. 



The bottom fauna has not been sampled from any of 

 the lagoons of Baja California, except San Quintin 

 (Barnard 1970). If bottom communities in the calving 

 lagoons are similar to San Quintin, gray whale feed- 

 ing should be common in Baja California. Laguna San 

 Quintin is located 300 km north of the first calving 

 lagoon, Guerrero Negro, and contains large numbers 



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