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Convention. An increase in the populations of these 

 species is desired. Because the age of first reproduc- 

 tion for some of these species has decreased, a faster 

 population recovery is possible. However, since baleen 

 whales are entirely dependent on krill for food, a large 

 krill harvest potentially would compete with whales for 

 food supply. Probability of competition is increased 

 since whale feeding and commercial harvesting would occur 

 in the same geographic areas and at the same time of year. 

 A reduction in food supply could cause a deterioration in 

 physiological condition and in turn raise the age of first 

 reproduction and slow the recovery rate of the populations. 

 Further, a decrease in reproductive rates could contribute 

 to a decrease in whale populations even without harvesting 

 of whales. 



Crabeater seals are also likely to be affected by a 

 krill harvest because they are very abundant and because 

 their diet is predominately krill. Because of their 

 abundance, crabeater seals are also the seal most likely 

 to be considered for commercial harvest. The impact of a 

 krill harvest should be mitigated by geographic separation. 

 Krill harvesting is most likely to occur in open waters 

 and crabeater seals inhabit the pack ice region. However, 

 juvenile seels, whose survival is critical to overall seal 

 population dynamics, may feed in open water or near the 

 edge of the pack ice, competing directly with the krill 

 fishery. 



Fish, birds and cephalopods which depend on krill as 

 a major item of the food supply will be affected by a krill 

 harvest. There is already evidence that bird populations 

 are increasing due to increased krill abundance resulting 

 from reduction in whale populations. Since harvesting will 

 reduce krill availability, populations of predators are 

 expected to decrease. Responses to a small krill harvest 

 will be difficult to observe. 



Ecosystem interactions are complex. The direct and 

 indirect impacts of harvesting on Antarctic populations 

 as discussed above reflect the dependence of population 

 size on food supply through a variety of mechanisms. 

 Because the Antarctic marine ecosystem is dynamic and has 

 already been under stress through harvesting of various 

 populations, especially baleen whales, other kinds of sys- 

 tem responses are possible. A change in the structure or 

 character of the ecosystem such as a shift to a copepod- 

 myctophid dominated food chain is possible. 



