dr = Pab 2PaE (C-5)
 dE

equal to zero and solving for E, the effort level corresponding to
maximum economic yield,


 E 1 (b ) (C-6)
 2 Pa

is obtained.

 Since r, P, and a are all positive constants, a comparison of
equations (C-3) and (C-6) illustrates that the effort level correspond-

ing to maximum economic yield is always less than that corresponding to

maximum sustainable yield.