-31- 



of the Convergence. Toothed whales eat fish and squid, 

 possibly penguins and juvenile seals (Mackintosh and 

 Brown, 1974; Laws, 1977a; Appendix H, BIOMASS, 1977). 



Fin, blue, humpback and southern right whales are pro- 

 tected from harvest. The present population size of fin 

 whales is about 20% of the original stock; blue whales are 

 about 5%, and humpback whales about 3%. The sperm whale 

 population is now about half of initial stock size and is 

 now harvested. Sei whales which are harvested in some 

 areas are presently slightly above half of initial popula- 

 tion size. Minke whales, also harvested, are still as 

 abundant as they were a century ago (Laws, 1977a). 



As population size of baleen whales species has de- 

 creased, there have been changes in other population para- 

 meters. Sexual maturity is reached at a younger age now 

 than when stocks were larger. The pregnancy rate is also 

 increasing. These changes combine to increase the growth 

 rate of the total population at low stock levels (Everson, 

 1977) . 



A growing population requires more food than a stable 

 population of the same size. Thus it is possible that if 

 whales were to expand populations to former levels, at some 

 point their food requirements would be greater than the 

 total food requirement of the original stock. 



C. Food Web 



The importance of krill in the Antarctic marine ecosystem 

 cannot be overemphasized. They are the most abundant zoo- 

 plankton species. They are the main herbivore in the Antarctic 

 marine ecosystem. Krill are the main food item for fish, 

 squid, penguins, crabeater and leopard seals, and fin, blue, 

 sei, humpback, and minke whales. Krill are present in the 

 diet of other seals as well. Killer whales and sperm whales, 

 in consuming fish and cephalopods and some seals, are only 

 one step removed from krill in the food chain. A food web 

 diagram for the Southern Ocean marine ecosystem is presented 

 in Figure 2. 



The dependence of many predators on one prey group, krill, 

 is a very unusual ecological situation. The swarming habit 

 of krill allows even very large predators to feed on them 

 efficiently. Removal of krill from the ecosystem by commer- 

 cial harvesting will compete directly with those predator 

 populations feeding in the same geographic area and indirectly 

 with other predators as overall abundance changes. 



