-108- 



Such questions must be given serious consideration as plans 

 for conservation and fisheries are developed. 



Several studies have shown that dramatic shifts and 

 fluctuations in community structure occur in response to 

 various combinations of ecological pressures (Dayton, 1975; 

 Dayton et al., 1970, 1974; Schaefer, 1970; Paine and Vaas , 

 1969; Estes and Palmisano, 1974; Simenstad et al., 1978). 

 These studies demonstrate that ecosystems and communities 

 are subject to impacts at a variety of levels, and depending 

 on the relative stability of the system, marked changes may 

 occur in the total community. Botkin and Sobel (1977) 

 discuss the concept of ecosystem stability, making the point 

 that we usually think of them as being relatively stable if 

 left alone from human interference. On the other hand, there 

 is much evidence that ecosystems in fact vary quite a bit 

 within normal boundaries due to a variety of environmental 

 factors. These authors cite Lack's (1954) examples of 

 animal populations which fluctuated widely. We have little 

 information about long-term population abundance levels for 

 many wild animal populations, so it is difficult to estimate 

 the actual extent of these fluctuations — particularly for 

 marine mammals. These authors state that if the ecosystems 

 fluctuate naturally, then the carrying capacity and optimum 

 sustainable populations (OSP) within these systems will also 

 vary. Such variations demand that management of living 

 resources be tuned to all sides of the ecosystem. 



Any krill harvest will impact the ecosystem to some 

 degree. When weighing the relative consequences of various 

 levels of harvest, one must ask what magnitude of krill 

 exploitation will cause significant shifts in the trophodynamics 

 of the ecosystem? Our present understanding of natural 

 ecosystem relationships is insufficient to allow prediction 

 of system sensitivity to manipulation of its food web 

 foundation. Major krill exploitation may disrupt all higher 

 levels of the food web, extending beyond individual faunal 

 stocks back to the krill themselves. In light of the uncertainties 

 associated with our knowledge of ecological mechanisms 

 operating in the Antarctic, one is forced to speculate on 

 possible impacts, acknowledging that ecosystem interactions 

 are subtle and highly complex. Relationships may exist of 

 which we are totally unaware. One can say with certainty, 

 however, that krill is a fundamental unit within the ecosystem 

 upon which a large number of species depend. In calculating 

 the consequences of our actions, we must bear this critical 

 fact in mind. 



