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2. Potential Levels of Impact 



With the specific case of krill exploitation, one can 

 identify at least three levels in the ecosystem where 

 harvest impacts might be felt. Impacts may affect target 

 species, dependent and related species, and relationships 

 throughout the ecosystem. 



Perhaps the most obvious direct impact on krill through 

 harvest would result from over-fishing to the point where 

 harvests might exceed the stock recruitment required to 

 maintain a viable population. Hazards of over-harvest must 

 be considered in relation to the possibility of krill 

 subpopulations requiring individual management plans. 

 Because of the suggestions presented earlier about the 

 existence of such separate stocks, care should be taken to 

 identify and conserve discrete stocks. 



Development of a commercial krill fishery might also 

 affect krill predators. The removal of major food competitors 

 (great baleen whales) allowed greater utilization of krill 

 by other whales and consumers such as seals, birds, fish, 

 and squid. It is not unreasonable to assume that a krill 

 harvest would have an opposite effect on these dependent 

 groups. Rather than increasing the availability of krill, 

 harvest would decrease the food available and increase the 

 degree of competition among krill predators. 



Species which feed directly on krill would not be the 

 only groups impacted through reduction in krill stocks — 

 some krill predators are in turn eaten by other carnivores 

 such as toothed whales, seals, birds, and other fish. For 

 example, fluctuations in krill abundance may affect some 

 squid populations which are important food items for Weddell 

 seals and elephant seals. Impacts at this level are difficult 

 to predict because the particular species affected will 

 depend on the results of competition between krill predators. 

 Therefore, when considering indirect impacts of krill 

 harvest, it is important to consider the variety of trophic 

 pathways through which impacts on target species can be 

 conveyed to other levels of the food web. Krill harvest 

 must be carefully regulated in order that other members of 

 the marine ecosystem are not adversely affected, either 

 directly by reduced food supply, or indirectly by competition 

 with other predators for the reduced krill stock. 



A third impact of a krill harvest might be the upsetting 

 of basic interrelationships in the ecosystem itself. For 

 example, the increased ship traffic associated with a fishery 

 might affect important spawning regions for fish and krill 

 damaging stocks through polluting the ocean. Likewise, 

 shore support stations could harm local terrestrial and 



