87


where Xli and X21 are, respectively, average crew size and average
 th
vessel size in the ith state. Several iso-fishing power contours are

shown in Figure 12. The rate of substitution necessary to maintain a

constant level of fishing power depends not only on the ratio of vessel

size to crew size on a given contour, but also on the location of the

contour (Figure 12). Consider point A on the Ep = 1.5 contour. An in-

crease in crew size of one man requires a decrease in vessel size of

approximately 10 gross registered tons to maintain fishing effort at a

constant level (point B). Next, consider point A' on the Ep = 2.0

contour. A one man increase in crew size now requires a decrease in


 80
 70 -A'

 6 60
 N W
 S. 50 -

 S.- 40 A E = 3.0
 "I ) p
 os-\
 > 30 = 2.5

 0 Ep = 1.5
 0 Ep = 1.5
 SEEp = 1.0

 0 2 3 4 5 6 7 8 9 10 11 Crew Size


 Figure 12. Iso-fishing power contours for selected levels of
 relative fishing power4



 The contours are expressed in terms of the fishing power index
described in equation (76). This changes only the scale of measure.
The contours shown in the figure ignore any technological limitations on
substitution. Thus, the ranges of substitution shown in all probability
exceed the limits of the feasible range of substitution. For example, a
10 ton vessel with 11 crew is clearly an infeasible input composition
for the fishery.