F-35 



derived the general equation below comparing the relative merits in terms of value of har- 

 vesting the predator or prey species: 



n n 



I V E' K. wi > Z V. E. V. 



V,V' = Value per unit weight of prey and predators respeotiirely 



E,E' = Exploitation rate of prey and predators respectively 



k = Conversion ratio prey to predator 



w,w = Mean wei^t of individual items eaten and in the catches respectively 



The summation is over all prey species. 



In the form that the equation is written here the greatest value would result from 

 harvesting the predator. 



With only sli^t rearrangement this general ecfuation may be applied to the krill/whales 

 type situation. In this case there is only one prey species but several predators. Using 

 the same notation except that the summation is over the different predator species (whales, 

 seals, etc.) the equation then becomes: 



n 



I V! EI K . W, > V E v7 

 7 i 1 1 i 



Implicit in this equation is the fact that, as Gullajid pointed out, the efficiency of 

 utilization (K) should be greater than the product of the relative value, the relative 

 exploitation and the probable growth of the prey. 



In this equation a lot clearly depends on the relation between V and V and K. Gulland 

 (1974) suggeststhat the overall conversion efficiency of krill to v/hales is verj-- low and of 

 the order of 2/^ and suggests that if the problem facing the world were of more food at all 

 costs, and the choice were between 1.7 million tons of whales, and 100 million tons of krill, 

 there would be no doubt that preference would have to be given to harvesting krill. Clearly 

 this represents an extreme case which in reality seems unlikely to occur. Betv;een these two 

 extremes there are an infinite number of potential answers particularly if the other exploit- 

 able resources are included into the analysis. The problem then reduces to one of making 

 management decisions to utilize and at the same time safeguard the resources. 



An alternative indirect method of harvesting krill has been proposed by Joyner _et al. 

 (1974) who suggest that the West Wind Drift is a suitable environment for salmon (see also 

 Hardy 1975, Joyner 1976). On the basis of published information on seasonal sea temperature 

 and the distribution of krill they consider that salm6n fry released from Southern South 

 America could search out and feed on krill in the Antarctic. Because of the known fast 

 growth rate of salmon they estimate that a salmon fishery of several million tons could be 

 established in the Tierra del Fuego area. They point out the obvious advantage of such a 

 system that since the salmon will probably return to their area of release the expense 

 involved in fishing will be minimal. However, from the inf oiTnation tliey give it seems un- 

 likely that the salmon will feed on krill since the main concentrations are south of the 

 area regarded as seasonally acceptable to salmon (Fig. 6.8 which is derived from information 

 in Joyner et al; 1974) • 



