29


 61 Tr Tr > 0
 S= { o (18)
 62r ir < O
where 9 = dV
 where 6, 62 are constants of proportionality and = firm

profit. Equation (18) illustrates that the entry and exit of firms is

asymmetrically proportional to profit. Generally, it is assumed that

firms leave the industry at a slower rate than firms enter.

 Equations (17), (17a), (17b) and (18) provide a system of equations

in which the entire workings of the fishery can be analyzed.

Specifically, equations (17a) and (17b) provide unique values of catch

and mesh size for any given population size and industry size. Thus,

once the catch rate per vessel and mesh size is determined, changes in

industry output can be seen to be a function of changes in the industry

size and stock size. These effects are summarized by

 X = F(X, V) (19a)

 V = I(X, V) (19b)

Equation (19a) states that the change in the resource stock over time is

a function of both the stock size and the number of efficiently operat-

ing vessels in the fishery. When X = 0, a biological equilibrium occurs

in the sense that the industry harvest rate is equal to sustainable

yield. In equation (19b), the change in the number of participating

vessels is also seen to be a function of stock size and industry size.

The set of solutions represented by V = 0 correspond to those in which

investment in the fishery is in equilibrium in relation to alternative


 Industry size here refers to the number of efficiently operating
vessels in the fishery.