OLIVER ET AL : GRAY WHALE FEEDING GROUNDS 



where walrus feeding excavations were common (Fig. 

 2) (Oliver et al. 1983). 



No gray whale feeding excavations were observed in 

 Baja California, despite a large number of survey 

 dives (Fig. 1) and better water clarity than the Bering 

 Sea. Although the currents were relatively strong in 

 many of the lagoons, other excavations and sediment 

 structures were maintained in the surface sediments. 

 For example, a large number of excavations pro- 

 duced by feeding rays was observed. These pits per- 

 sisted in a number of lagoon habitats, but were 

 usually found in the intertidal and shallow subtidal 

 areas where gray whales did not occur. Rays were ob- 

 served creating pits on several occasions. Qualitative 

 bottom samples commonly revealed large bivalves, 

 especially Chione spp., in areas where ray pits oc- 

 curred. Dense infauna and other patches of potential 

 gray whale prey did not occur in the ray feeding 

 areas. 



Infaunal Prey 



The abundance of infaunal invertebrates in the gray 

 whale feeding grounds of the Bering Sea was only 1.5 

 times greater than the total abundance of animals in 

 the calving lagoons, which included Guerrero Negro, 

 Ojo de Liebre, and San Ignacio (Fig. 4). However, am- 

 peliscid amphipods were never abundant in the calv- 

 ing lagoons, while A. macrocephala dominated the 

 Bering Sea fauna (also see Neiman 1963 and Stoker 

 1978). The abundance of infaunal crustaceans and A. 

 macrocephala in the gray whale feeding grounds (Fig. 

 2) was as high as 67,746/m 2 and 21,448/m 2 , re- 

 spectively. Infaunal abundance was highest in San 

 Quintin, the most northerly lagoon surveyed in Baja 

 California (Fig. 4). Here we sampled from dense beds 

 of A. agassizi, which accounted for 95% of the total 

 individuals and occurred in abundances as high as 

 135,912/m 2 . 



In contrast to abundance, the biomass of the in- 

 fauna was 20 times greater in the Bering Sea than in 

 the calving lagoons (Fig. 5). Over 70% of the biomass 

 in San Quintin was A. agassizi, and the total biomass 

 was more than half of the Bering Sea value (Fig. 5). 

 However, the Bering Sea data were averaged over a 

 large group of stations sampled by Stoker (1978). 

 The value shown for San Quintin was the densest 

 Ampelisca bed we observed. 



Most of the benthic invertebrates living in the 

 southern lagoons were quite small. This was clearly 

 reflected in the biomass data (Fig. 5). In addition to 

 the rarity of large species and individuals, deposit 

 feeders also were relatively rare among the 

 polychaete worms, especially in the unvegetated 



sedimentary habitats. For example, a suspension- 

 feeding sabellid worm (probably Fabricia) was the 

 only species that occasionally occurred in relatively 

 high abundance (maximum of 250 in a 0.0075 m 2 

 core). This species was usually < 5 to 6 mm long, and 



3000 



2955 ±266 



TOTAL INFAUNA 



I I I 



BERING SAN LAGUNA OJO ESTERO SAN SCAMMON'S 

 SEA QUINTIN MANUELA DE COYOTE IGNACIO OFFSHORE 

 LIEBRE 

 8 3 6 23 9 6 8 



FIGURE 4. — Abundances of total infaunal invertebrates, crus- 

 taceans, and polychaete worms in the gray whale feeding grounds of 

 the Bering Sea and in Baja California. Means and standard 

 errors. 



60O! 



coo 



BIOMASS 



200 



BERING 

 SEA 



SAMPLE NUMBER 28 



SAN LAGUNA OJO D£ ESTERO SAN OFFSHORE 

 QUINTIN MANUELA LIEBRE COYOTE IGNACIO SCAMMON'S 



23 



FIGURE 5. — Wet weight biomass of the total infauna from the gray 

 whale feeding grounds in the Bering Sea (from Stoker 197.S) and in 

 Baja California. Means and standard errors. 



517 



