Fishing effort 



Figure 4. — Alternative yield curves for a fish stock exploited at variable levels 



of fishing effort. 



as such a limit cannot be overstepped without 

 economic losses. 



It could also be added that the impossibility 

 of constructing complete bioeconomic models is 

 not as harmful as might be thought. In many 

 cases of advanced overfishing, complete bio- 

 economic models would not necessarily supply 

 practical management policies. In a situation 

 of advanced fishing effort, the benefits to be 

 expected from fishery management are benefits 

 which could not be reaped before the stock is 

 rebuilt to its MSY level. In the meantime the 

 reductions likely to be made in fishing effort 

 would cause problems of de-investments (e.g., 

 scrapping premiums . . .) and of employment 

 (re-employment of the fishermen concerned). 

 Furthermore, a reduced and less costly fishing 

 effort exploiting a rebuilt stock would give 

 rents; it is possible to imagine regulatory means 

 by which such rents would be at least partly 

 taken from the remaining fishermen, but this 

 could only be made on the basis of the fishing 

 techniques prevalent at the time of making the 

 regulation. It would often be difficult to find 

 the regulations which would result in the desir- 

 able aggregate effort while pei'mitting new 

 technological developments at the same time. 

 Some success has been achieved in the Canadian 



salmon program toward attaining both of these 

 ends. In other words, even if complete bio- 

 economic models would exist they would not 

 as such provide complete solutions to the 

 problems of re-establishing overfished stocks to 

 the ideal situation of MSY. 



Before going further it is necessary to say a 

 few words about the techniques of communica- 

 tion between biologists and economists. In fact, 

 there is not much difficulty with the basic 

 Schaefer model which is widely used in the 

 United States. Its mathematical expression is 

 as follows: 



(1) Y = aE + bE^ 



where 



Y = yields, expressed in weight of 



catches 

 E = fishing effort, expressed in 



number of given vessels during 



given times 

 a,b = parameters characterizing 



each particular stock. 



The economist has little difficulty in following 

 and utilizing biological results from this model. 



100 



