MANAGEMENT O F FISHERY RESOURCES
23
maximum catch may be taken with only SOYo of the effort required to
take the maximum, and the cost per ton of taking the last 2% would
be around ten times that of taking the first 98%. Blmost certainly the
resources in ships, men and money in taking the last 2% would be
much better employed elsewhere-even when the demand is for fish
a t almost any cost there are likely to be alternative and relatively
unexploited stocks t o which the surplus effort could be diverted. So
long as alternative underfished stocks exist the apparent contradiction
between the biological objective of greatest physical yield, and the
economic objective of greatest economic yield (cf. Christy and Scott,
1965, p. 219) is valid only if consideration is restricted to the individual
heavily fished stock. The greatest physical yield from the oceans as a
whole will be possible only if the presently overfished stocks are
harvested as efficiently as possible.
The objective, therefore, of rational management should be to
maintain the fishing effort a t the level giving the greatest net returns
(value of catch less cost of capture), i.e. at the level where the marginal
cost of adding one unit of effort (one extra vessel) is just equal t o the
marginal value of the increase in hhe sustained catch resulting from the
extra effort, rather than the marginal value being zero (if the effort is
at the level giving the maximum sustained yield), or even negative (if
the effort is past the maximum). This is shown diagrammatically in
Fig. 10, in which the curve in Fig. 9 relating catch (in terms of weight)
to the amount of fishing (basically in terms of the proportion of the
stock removed per year) is replaced by a curve relating value of the
catch to the cost of catching it. To a first approximation the value of
the catch is proportional t o the weight caught, and the cost is proportional t o the amount of fishing. Then the equilibrium position is the
point A where the line of equal costs and value cuts the curve. I n this
example it is beyond the level of fishing which gives the maximum
catch, A,, and a reduction of fishing to produce the maximum sustained
yield will also produce a surplus of value over costs equal t o A,&.
However, a further reduction of fishing to bring the catch to the point
A , will produce an even bigger surplus A$,. This simple statement of
the immediate economic aspects of management becomes more complex
when considering several stocks of fish, or fishing carried out by several
countries. Since each country will have different costs, and set different
values to the fish, the optimum position for each country will be
different. However, if two countries have been fishing the same stock
for some time, without great changes, both will presumably have about
the same equilibrium position, so that their optimum positions will
also be similar. I n any case, if the total effort has increased beyond the
A.M.B.-6
2
23
maximum catch may be taken with only SOYo of the effort required to
take the maximum, and the cost per ton of taking the last 2% would
be around ten times that of taking the first 98%. Blmost certainly the
resources in ships, men and money in taking the last 2% would be
much better employed elsewhere-even when the demand is for fish
a t almost any cost there are likely to be alternative and relatively
unexploited stocks t o which the surplus effort could be diverted. So
long as alternative underfished stocks exist the apparent contradiction
between the biological objective of greatest physical yield, and the
economic objective of greatest economic yield (cf. Christy and Scott,
1965, p. 219) is valid only if consideration is restricted to the individual
heavily fished stock. The greatest physical yield from the oceans as a
whole will be possible only if the presently overfished stocks are
harvested as efficiently as possible.
The objective, therefore, of rational management should be to
maintain the fishing effort a t the level giving the greatest net returns
(value of catch less cost of capture), i.e. at the level where the marginal
cost of adding one unit of effort (one extra vessel) is just equal t o the
marginal value of the increase in hhe sustained catch resulting from the
extra effort, rather than the marginal value being zero (if the effort is
at the level giving the maximum sustained yield), or even negative (if
the effort is past the maximum). This is shown diagrammatically in
Fig. 10, in which the curve in Fig. 9 relating catch (in terms of weight)
to the amount of fishing (basically in terms of the proportion of the
stock removed per year) is replaced by a curve relating value of the
catch to the cost of catching it. To a first approximation the value of
the catch is proportional t o the weight caught, and the cost is proportional t o the amount of fishing. Then the equilibrium position is the
point A where the line of equal costs and value cuts the curve. I n this
example it is beyond the level of fishing which gives the maximum
catch, A,, and a reduction of fishing to produce the maximum sustained
yield will also produce a surplus of value over costs equal t o A,&.
However, a further reduction of fishing to bring the catch to the point
A , will produce an even bigger surplus A$,. This simple statement of
the immediate economic aspects of management becomes more complex
when considering several stocks of fish, or fishing carried out by several
countries. Since each country will have different costs, and set different
values to the fish, the optimum position for each country will be
different. However, if two countries have been fishing the same stock
for some time, without great changes, both will presumably have about
the same equilibrium position, so that their optimum positions will
also be similar. I n any case, if the total effort has increased beyond the
A.M.B.-6
2