-53- 



essential to describing seals' predatory pressure on the 

 ecosystem (Figure 18) . 0ritsland (1977) reviewed the food 

 consumption of various species of pack ice seals. In 

 general, he found that crabeater seals consume mainly krill 

 with some supplemental fish; leopard seals take fish, krill, 

 penguins, caphalopods; Ross seals consume mainly cephalopods 

 and fish; and Weddell seals, when they are present in the 

 pack ice, eat primarily fish and cephalopods. Tables 9, 10, 

 and 11 show 0ritsland's estimates of food types and amounts 

 for each species. Coupled with biomass estimates, total 

 annual consumption for each species can be estimated. In 

 contrast to baleen whales (except minke whales) which spend 

 only several months a year feeding in the Southern Ocean, 

 these seals always remain south of the Convergence. Since 

 seals can be assumed to be eating year-round except for 

 minor seasonal fasting (0ritsland, 1977) , the resultant prey 

 consumption is rather large. 



1) Crabeater Seals 



The crabeater seal diet consists primarily of krill 

 (94% as reported by 0ritsland, 1977), 3% fish, 2% cephalopods, 

 and 1% miscellaneous invertebrates. A specialized dental 

 pattern, present in few other mammals (less specialized 

 dentition is also seen in leopard seals) , forms a seive when 

 the jaws are closed and allows crabeater seals to feed 

 heavily on krill. 



2) Leopard Seals 



Remains of krill, squid, fish, penguins, and seals have 

 been found in leopard seal stomachs. Although penguins are 

 often considered a major leopard seal food source, this 

 conclusion is probably biased because of the extensive 

 observations made near penguin rookeries (Brown, 1957; 

 Penney and Lowry, 1967; Muller-Schwarze , 1971; Muller-Schwarze 

 and Muller-Schwarze, 1971; Dawson, 1974). Hamilton (1939) 

 and Laws (1964) showed that leopard seals also utilize fish 

 and squid while Hofman et al. (1977) observed leopard seals 

 feeding on krill even though large numbers of adelie penguins 

 were nearby. Llano (pers. comm.) observed the feces of 19 

 leopard seals on ice floes in January, 1974. Eighteen had 

 been feeding on krill and one on penguins in an area 

 frequently traversed by penguins. There are also reports 

 of leopard seals eating other seal species (Wilson, 1907; 

 Bertram, 1940; Laws, 1964; Gilbert and Erickson, 1977) in- 

 cluding fur seals (Rankin, 1951) , Weddell and crabeater 

 seals (Mawson, 1915; Hamilton, 1939; Mackintosh, 1967; 

 Erickson and Hofman, 1974) . Siniff and Bengtson (1977) 

 hypothesized that the scars commonly seen on crabeater seals 



