C-19 



south C'f the Convergence was estimated. The bulk of this 

 biomass is Adelie penguins which subsist primarily on krill. 

 Antarctic birds consume 67 times their body weight per year, 

 .for a total prey consumption estimate of 18 x 10 tons. 

 Proportions of krill and other species in bird diets were 

 given for the Antarctic and subantarctic regions combined. 

 Correcting these ratios to allow for the dominance of Adelie 

 penguins south of the Convergence, birds consume 14 . 4 x 10" 

 tons of krill annually. 



Because birds are easy to census, since they breed in 

 colonies and in accessible land areas, the bird biomass and 

 consumption data are very reliable. 



Birds have a relatively large impact on the ecosystem 

 in proportion to their standing stock because of their high 

 consumption rates. However, compared to seals and other 

 species as krill consumers, birds have a relatively small 

 impact. However, penguins may prove to be useful indicators 

 of krill abundance (Green, 1975). Data on penguin popula- 

 tion size and breeding success can provide an important key 

 to the condition of krill standing stocks. Birds are much 

 easier to sample than are zooplankton. 



Crabeater seals . Crabeater seals are by far the most 

 abundant of Antarctic seals. Population estimates vary 

 from 15 million individuals (Laws, 1977) to between 20 and 

 30 million individuals (Hofman, conversations at Woods Hole 

 Conference) to estimates of 30-70 million individuals 

 (Erickson, et al . , 1971). For the rest of the paper, cal- 

 culations use 25 million indiiriduals or 5.5 x 10^ tons of 

 crabeater seals. 



Using an annual consumption rate of 23.45 times ave- 

 rage body weight (Oritsland, 1977), total consumption by 

 crabeater seals is 111 x 10^ tons of food. Since their 

 diet is 94% krill (Laws, 1977), they eat 106 x 10^ tons of 

 krill annually. 



Biomass estimates for other seals are from Laws (1977) 

 and Hofman (discussions at Woods Hole Conference). Total 

 biomass estimated for other seals is 0.8 x 10 tons (com- 

 Dared to a total of 5.5 x 10^ tons for crabeater seals 

 alone). Other seals consume a total of 18.7 x 10° tons 

 per year of which 3.1 x 10 are krill (after Laws, 1977). 



Whales . Baleen whales found south of the Convergence 

 are blue fin, humpback, sei , and minke whales. Fin whales 

 are the '?:^st abundant with a total estimated biomass of 4 

 X 10^ tc:^. Minke vjhales , although less abundant, consume 

 more bec-^.:se they feed for a longer period of time in the 



