Fish Population Dynamic and Stock Assessment

6.1.3.1. Schaefer model

The catch per effort or yield per unit of effort is designated as Y/f. The Y/f is a function of effort, ‘f’. MSY could be computed from the following equation.

$$Y(i) \over f(i)$$ = a + b x f(i) ----------------------------------------------------> (1)

In Schaefer model, the slope ‘b’ will be negative if the catch per unit of effort ‘y/f’, decreases for increasing effort. This model implies one effort level for which ‘y/f’ value obtained just after the first boat fishes on the stock for the first time. Hence, the intercept value is positive. Thus ‘- a/b’ is positive and ‘y/f’ is zero for f = -a/b. As the negative value of catch per unit effort, ‘y/f’ is will not be a reality, this model applies to f values lower than ‘- a/b’. For unexploited stock or for stock which is less exploited, this model could be used. Even at very few levels of effort, the straight line reaches zero and attains annihilation.