18
J. A. CULLAND AND J. E. CARROZ
however, the total numbers caught, and the total weight, are small.
Equally at very high rates of fishing, applied as soon as the fish are big
enough to be caught, although the numbers caught will be very large,
they will not survive long enough to grow much, so that the total catch
will be only moderate, consisting of very small fish. The greatest catch
from a given brood is taken by allowing the fish to grow to a reasonable
size, either by only fishing moderately hard or by using some selective
gear (e.g. trawls with large meshes) which will only catch the larger
fish, allowing the small ones to escape and grow. In addition, it is not
improbable that the average number of young produced by the low
stocks when fishing is heavy will be less than those produced from
larger stocks, although this is not as obvious as it may seem. Most
marine fish produce very large numbers of eggs (sometimes millions), so
that even a very small adult stock could produce a large brood, and
evidence from some stocks shows that the adult stock can be reduced
substantially without any significant reduction in the number of young
produced which recruit to the fishery in later years (Beverton, 1962).
The number of young produced each year often fluctuates very widely
quite independently of changes in the adult stock, and these fluctuations
make it very difficult within any particular stock of fish to determine
whether a reduction in the number of adults results, on the average, in
any significant reduction in the number of young. This uncertainty has
often, in practice, led to the assumption that the number of recruits is
independent of the adult stock, i.e. that there is no need for regulatory
measures to maintain the adult stock. However, this assumption can
lead to disaster for the fishery if in fact it is false. The obvious example
of the disasters following a failure to maintain an adequate breeding
stock is that of the Antarctic whales. Since they are mammals, producing only one young every other year, there is no doubt that a
reduction in the adult stock would result in fewer young animals
recruiting to the future stock. Under proper management these
Antarctic stocks could maintain annual catches of around 6 000 blue
whales and 20 000 fin whales : a t present the blue whales have had to be
given complete protection, but even if hunted intensively only a few
hundred could be caught (Chapman et al., 1964, 1965). I n the 1965-66
season only 2 300 fin whales were caught, and even this small total will
only allow the depleted fin whale stock to rebuild rather slowly. Thus
failure of proper management has meant a loss in annual catch of 6 000
blue whales, and 18 000 fin whales, which would have yielded about a
quarter of a million tons of oil, and equivalent quantities of whale meat
and other by-products. Similar disasters to fish stocks are less well
established, but a possible example is the California sardine (Xardinops
J. A. CULLAND AND J. E. CARROZ
however, the total numbers caught, and the total weight, are small.
Equally at very high rates of fishing, applied as soon as the fish are big
enough to be caught, although the numbers caught will be very large,
they will not survive long enough to grow much, so that the total catch
will be only moderate, consisting of very small fish. The greatest catch
from a given brood is taken by allowing the fish to grow to a reasonable
size, either by only fishing moderately hard or by using some selective
gear (e.g. trawls with large meshes) which will only catch the larger
fish, allowing the small ones to escape and grow. In addition, it is not
improbable that the average number of young produced by the low
stocks when fishing is heavy will be less than those produced from
larger stocks, although this is not as obvious as it may seem. Most
marine fish produce very large numbers of eggs (sometimes millions), so
that even a very small adult stock could produce a large brood, and
evidence from some stocks shows that the adult stock can be reduced
substantially without any significant reduction in the number of young
produced which recruit to the fishery in later years (Beverton, 1962).
The number of young produced each year often fluctuates very widely
quite independently of changes in the adult stock, and these fluctuations
make it very difficult within any particular stock of fish to determine
whether a reduction in the number of adults results, on the average, in
any significant reduction in the number of young. This uncertainty has
often, in practice, led to the assumption that the number of recruits is
independent of the adult stock, i.e. that there is no need for regulatory
measures to maintain the adult stock. However, this assumption can
lead to disaster for the fishery if in fact it is false. The obvious example
of the disasters following a failure to maintain an adequate breeding
stock is that of the Antarctic whales. Since they are mammals, producing only one young every other year, there is no doubt that a
reduction in the adult stock would result in fewer young animals
recruiting to the future stock. Under proper management these
Antarctic stocks could maintain annual catches of around 6 000 blue
whales and 20 000 fin whales : a t present the blue whales have had to be
given complete protection, but even if hunted intensively only a few
hundred could be caught (Chapman et al., 1964, 1965). I n the 1965-66
season only 2 300 fin whales were caught, and even this small total will
only allow the depleted fin whale stock to rebuild rather slowly. Thus
failure of proper management has meant a loss in annual catch of 6 000
blue whales, and 18 000 fin whales, which would have yielded about a
quarter of a million tons of oil, and equivalent quantities of whale meat
and other by-products. Similar disasters to fish stocks are less well
established, but a possible example is the California sardine (Xardinops