24
J. A. CULLAND AND J. E. CARROZ
c o s t s
FIG. 10. The relation between costs of fishing and value of the catch. Point A , where
the line of equal costs and values cuts the curve, is the equilibrium position without
regulation. The greatest net return, A,-B,, is obtained by limiting fishing to about
one-third of the equilibrium level.
level giving the maximum catch, it will be in the interest of all to
reduce the effort, even if the magnitude of the reduction in the effort
required to reach the various optimum positions may be different.
Difference in national interests, and indeed differences between
different groups of fishermen in the same country, are likely to be more
serious when several stocks of fish of different species are concerned.
No species of fish exists in isolation, but may compete with one species
for food, be eaten by a second, and feed on a third, and all these stocks
may be exploited by different fishermen whose catches will therefore
interact. Also fishermen, while catching one species, may incidentally
catch another species which is of primary interest to some other fishermen ; for example, in the North Sea, vessels trawling for herring often
catch numbers of small haddock (Sahrhage, 1959). In such situations it
is normally impossible to take the maximum sustainable yield of all
the species being exploited : for instance, the maximum yield of haddock
would only be taken if no small haddock were killed by herring trawls,
which could only be achieved by prohibiting trawling for herring, and
this would reduce the catch of herring (I.C.E.S., 1960). Thus, a unique
objective of management cannot easily be defined, though the biologist
can, a t least in principle, calculate what the effects of possible regulatory action would be, and hence those regulations can be introduced
J. A. CULLAND AND J. E. CARROZ
c o s t s
FIG. 10. The relation between costs of fishing and value of the catch. Point A , where
the line of equal costs and values cuts the curve, is the equilibrium position without
regulation. The greatest net return, A,-B,, is obtained by limiting fishing to about
one-third of the equilibrium level.
level giving the maximum catch, it will be in the interest of all to
reduce the effort, even if the magnitude of the reduction in the effort
required to reach the various optimum positions may be different.
Difference in national interests, and indeed differences between
different groups of fishermen in the same country, are likely to be more
serious when several stocks of fish of different species are concerned.
No species of fish exists in isolation, but may compete with one species
for food, be eaten by a second, and feed on a third, and all these stocks
may be exploited by different fishermen whose catches will therefore
interact. Also fishermen, while catching one species, may incidentally
catch another species which is of primary interest to some other fishermen ; for example, in the North Sea, vessels trawling for herring often
catch numbers of small haddock (Sahrhage, 1959). In such situations it
is normally impossible to take the maximum sustainable yield of all
the species being exploited : for instance, the maximum yield of haddock
would only be taken if no small haddock were killed by herring trawls,
which could only be achieved by prohibiting trawling for herring, and
this would reduce the catch of herring (I.C.E.S., 1960). Thus, a unique
objective of management cannot easily be defined, though the biologist
can, a t least in principle, calculate what the effects of possible regulatory action would be, and hence those regulations can be introduced