n 



equilibrium with its environment. When at its maximum size, the popu- 

 lation is said to have saturated the environment. At this point, additions 

 to the populations from growth or recruitment are offset by natural losses. 

 The dome-shaped surplus production and spawner-recruitment models... are 



examples of theories that assume the surplus production or recruitment 



(19) 

 is dependent on the size of the exploitable population..." 



6. Density dependent effects 



"If the stock increases, e.g., following a reduction in fishing, the 

 likely effects are that natural mortality will increase, and the growth 

 decrease, but that recruitment will increase. These effects act in 

 opposite directions, the first two reducing the yield at high stock levels 

 (i.e., at low fishing intensities, or with a large mesh size), but the 

 last increasing the yield under these conditions of fishing." 



7. Depletion 



A stock is considered to be depleted according to two possible de- 

 finitions. In one, a fishery is considered to be depleted when the yield 

 from that fishery is on the right-hand slope of the yield curve (Figure A). 



MSY 



yield 



depleted 



effort 



A second definition relates depletion to the relationship between 

 adults in the stock and recruitment: (Figure B) 



