10 



3. Potential yield 



"Within each resource the potential yield is determined by its 

 absolute size (weight) as a function of the number of fish in the resource 

 and the growth potential of the individual fish. In general, the larger 

 the habitable area available to a stock, the bigger the stock is... 

 The number of fish in a resource is governed by the balance between re- 

 cruitment (numbers of young fish entering the stock each year) and the 

 death rate from fishing or natural causes... Experience to date is that 

 within each resource--apart from a few severly depleted ones— recruitment 

 fluctuates without trend; nor is there any evidence of trend in the rate 

 of natural death. Given these parameters, the yield realized from the 

 resource depends upon the rate of exploitation in relation to the growth 

 potential of the fish concerned... As a very broad generalization, one 

 may expect fast-growing fish to have a relatively shorter lifespan and 

 vice versa." ' 



4. Basic productivity 



Potential fisheries production from a region can be defined as the 



harvest which can be taken by man (as a predator) on a continuing basis 



(18) 

 operating at a given trophic level or combination thereof.^ ' 



5. Biological surplus 



"A variety of models have been developed to quantify the surplus 



or growth potential of fisheries populations. Most assume that the sur- 

 plus production will increase steadily until the population size reaches 

 intermediate level, then will decline until the population comes into 



