H-27 



RESEARCH PROGRAMMES 



skuas, but their low numbers and biomass render them relatively insignificant in the ecosystem. 

 Their primary effect, with the exception of the terns, is by their scavenging within the rookeries 

 of seals and other sea birds. 



The importance of sea birds in the Antarctic ecosystem lies largely in their role as 

 consumers. According to more or less empirical calculations on different species, the Antarctic 

 and sub-Antarctic regions contain at least 188 million birds with a total biomass of 577 000 

 tons (Table 3)'. 65 per cent of the stocks are distributed in the sub-Antarctic region 

 representing 55 per cent of the total biomass. The Spheniscklae determined from these figures 

 constitute 65 per cent of the stocks and 90 per cent of the biomass for the whole Antarctic 

 region. The birds are estimated to consume 39 million tons of food per year including 21 

 million tons for the sub-Antarctic region (54 per cent). The Spheniscidae alone consume 86 per 

 cent of the total. As consumers, birds are presently about equal in importance to the large 

 whales and about half as important as the seals. They consume a relatively small proportion of 

 the krill standing stock in summer when food is perhaps not a Umiting factor for them; on the 

 other hand, it is likely that winter plankton availability constitutes a major factor hmiting their 

 abundance. 



Table 3. Estimates of antarctic bird populations, 

 biomass, and food consumption 



Food consumption in Antarctic 

 and sub-Antarctic' 



33 173 



2 867 

 2 131 



427 



65 



39 000 



' Thousands of metric tons. 

 ^ Totals rounded. 



2.5.3 Interactions 



Direct interactions are thought to be hmited to the predator-prey relationships exhibited 

 by Killer Whales and Leopard Seals toward smaller marine mammals and penguins and those 

 exhibited by skuas and gulls toward other species. Preferences of various seal species (Ross, 

 Crabeater and Leopard) for different ice types may ease interspecific competition for space. 

 Although Elephant and Fur seals are both land breeders, their distribution overlap is reduced by 

 their occupying, at South Georgia for example, different habitats (sandy beaches by Elephant 

 Seals and rocky shores by Fur Seals) and by staggered pupping seasons. It is probable that 

 behavioural interactions in relation to food resources occur. Odontocetes tend to be gregarious 

 while hunting and are known to communicate acoustically underwater. 



Indirect interactions through competition for the common food resources such as krill and 

 squids are considered to be more important. Despite the fact that for some groups, such as 



' Recent observations (British Antarctic Survey. 1977) at South Georgia indicate that the biomass of 

 Macaroni Penguins Eudyptes chrysolophus at the north-west end of the island alone is in excess of 

 100 000 tons. 



