Catch


 C*I '2
 ClI C
 SC P
 C3
 C2 I Sustainable
 Yield



 E2 El Effort

 Figure G-1. Resource stock adjustment for fixed effort
 levels


 The adjustment of the resource stock to the point where catch

equals sustainable yield is best described by means of graphic

illustration. The figure above contains a typical Schaefer type sus-

tainable yield function and a series of short run catch function. Each

short run catch equation is indexed by a resource stock level. For

example, the catch function Cpl corresponds to a stock size of P1.

 Assume that the resource stock size is P1 and that effort in the

fishery is given by E1. The corresponding catch, C1, represents an

equilibrium catch in that Cpl intersects the sustainable yield function

at El units of effort. Now suppose effort is decreased to E2 and

remains fixed at that level. Initially catch will decline along Cp

to a level denoted in the figure by C2. This level of catch, however,

is below sustainable yield, resulting in an increase in the resource