Goebel et al.: Diving patterns and foraging locations of female Callorhmus ursinus 



177 



Table 6 



The percent of stomachs with food of lactating northern fur 

 seals collected over the continental shelf (in water <200m 

 deep) and off the continental shelf (> 200 m deep). Collections 

 were made from July through September. 1958-74. 



Time (hours) 



Over the shelf 



Off the shelf 



0600-1000 

 1400-1900 



80.0 (403/504) 

 54.0 (277/513) 



95.3 (225/236) 

 39.7 (94/237) 



stomachs than females collected over the shelf (chi- 

 square, P<0.001). Afternoon samples showed a reverse 

 trend with a higher incidence of food in stomachs of 

 seals collected on the shelf than off the shelf (chi- 

 square, P< 0.001). 



Discussion 



Dive patterns and foraging locations 



The results of this study show that northern fur seal 

 females diving in deep water beyond the continental 

 shelf primarily exhibit the shallow-diving pattern and 

 dive predominantly at night. Females feeding at or 

 near the shelf break may exhibit both diving patterns. 

 Females located on the continental shelf (which had not 

 already completed their feeding trip) were more likely 

 to exhibit the deep-diving pattern and dived to depths 

 of greater than 75 m throughout the day and night. 

 However, females found over the continental shelf had, 

 at times, shallow dive bouts (<30m) at night. 



The pelagic fur seal database provided insight into 

 the relationship between diving patterns and feeding 

 locations of fur seals in the Bering Sea. If the deep- 

 diving pattern is associated with feeding on the con- 

 tinental shelf, and deep divers feed during the day, one 

 can test the hypothesis that females found over the con- 

 tinental shelf during the day have a greater probabil- 

 ity of having food in their stomachs than those females 

 found off the shelf, which would be diving predominant- 

 ly at night. The analyses of the northern fur seal pelagic 

 database support our finding that the deep-diving pat- 

 tern is associated with the continental shelf by show- 

 ing that females collected over the continental shelf 

 were more likely to be feeding during the day. 



Dive patterns and probable prey 



The feeding locations and dive patterns observed in this 

 study are consistent with the known distribution of fur 

 seal prey items. Kajimura (1984) summarized the varia- 

 tion in principal forage species for fur seals, depending 

 on location. Fur seals feeding in the Bering Sea beyond 

 the continental shelf over deep water fed on oceanic 

 squid of the family Gonatidae (primarily Goncitus spp., 

 Berryteuthis magister, and Gonatopsis borealis) or 

 deep-sea smelts of the family Bathylagidae. These prey 

 species, and fish with swim bladders, exhibit diel ver- 

 tical migration and are at relatively shallow depths at 

 night as they move vertically in synchrony with the 

 deep scattering layer (Roper and Young 1975, Pearcy 

 et al. 1977). It is during the night that they are fed upon 

 by fur seals which rarely dive beyond 200 m (Gentry 



