C-25 



KRILL HARVEST QUESTIONS 



Surplus Argument 



Mention of krill as a harvestable resource is invaria- 

 bly connected with an observation on the decline of whales 

 in this century. The argument is essentially that an amount 

 of krill equivalent to the difference between present con- 

 sumption and peak consumption by whales can be harvested. 

 Assumptions associated with this argument are that man can 

 exactly replace whales as a predator in the Antarctic eco- 

 system and that consequently harvesting will have no impact 

 on the rest of the system. This argument is no longer con- 

 sidered valid by scientists, but remains a part of the pub- 

 lic attitude on Antarctic resource potential. 



There are several very strong arguments against the 

 assumption that krill harvesting will not affect the Antarc- 

 tic marine ecosystem. First, harvesting can not exactly 

 replace whales as a predator. The fraction of the krill 

 population which the whales consumed, with a specific cir- 

 cumpolar distribution, time of year, size of krill removed, 

 and relationship to pack ice, will not be duplicated by 

 commercial harvesting. 



Second, there is evidence that the ecosystem has 

 already adjusted partially to the reduced whale population. 

 Penguins and some seal populations appear to have increased 

 to take advantage of more available krill (Conroy, 1975; 

 Laws , 19 7 7b) . 



A large commercial krill harvest will compete with 

 krill predators . V/ith the change in abundance of krill 

 available to the ecosystem, there will be changes in preda- 

 tor populations. It is suggested that populations will 

 return to 1900 levels -- i.e., to what they were when whale 

 populations were considerably higher (J. A. Gulland letter 

 to K. Green, September 1977). Population levels for fish, 

 cephalopods , birds and seals around 1900 are not known, 

 however. 



Yield Estimates 



The estimate of total predation on krill from Figure 

 3 is approximately 330 x 10 tons. Any commercial harvest 

 will be taken from those 330 x 10 tons. Harvesting will 

 displace some predators. 



Literature estimates of sustainable krill harvest 

 range from 70 to 150 x 10^ tons per year (Moiseev,- 1970; 



