MANAGEMENT OF FISHERY RESOCRCES
51
for food with a third, could be extended almost indefinitely, taking into
account the widely ranging movements of many species, so that the
scientist should set limits beyond which the possible interactions can,
€or practical purposes, be ignored.
Any assessment of the effect of proposed regulations, or of the
absence of regulations, must be subject to some degree of uncertainty,
so that complete scientific advice will include some indication of the
degree of uncertainty involved. The nature of the uncertainties is such
that statistical presentation of confidence limits, etc., are generally not
relevant, and the statement has to bc to some degree subjective,
including judgments on such things as whether a particular mathematical model is applicable to a given situation. The important question
is whether the relative advantages of different regulations (or no
regulation) will be changed. For example, calculations may show that
in a certain trawl fishery an increase in mesh size will result in an
immediate drop in catch in the first year of 5 2 % , followed by an
increase %Tithin three to four years to a level 4.7% above the original
level (i.c. regarding the small fish released as an investment, they will
nearly as a group double in weight). In fact, they may rather more
than double, making the gain perhaps S%, or the gain may be only
4%, but in any event the larger mesh will give a small gain, and advice
in that form can be given t o the regulatory body.
Another form of uncertainty is that many stocks fluctuate for
reasons quite independent of fishery, e.g. due to variation in year-class
strength (Hjort, 1914). In such fisheries the predictions made are
generally not of the actual catch in the future, but are comparisons of the
catch that would be taken if the proposed regulations were introduced,
with the catch taken if different regulations, or if none, were in force.
Proper management, therefore, requires good scientific knowledge
based on adequate data. They are essential for all stocks, not merely
those in immediate need of regulation, since one aspect of proper
management is to avoid unnecessary restrictions, and to be sure
of this requires a certain minimum supply of data. More important,
the proper understanding of a heavily exploited stock depends on
the comparison of the characteristics of the stocks (abundance, as
measured, say, by catch per unit effort, the proportions of different
ages and sizes, etc.) under heavy and light fishing, and therefore
requires adequate information from the period when fishing was
still light.
Though in any fishery a stage could be reached when the possible
benefits from improved management based on better scientific information will be less than the additional costs of getting that information,
51
for food with a third, could be extended almost indefinitely, taking into
account the widely ranging movements of many species, so that the
scientist should set limits beyond which the possible interactions can,
€or practical purposes, be ignored.
Any assessment of the effect of proposed regulations, or of the
absence of regulations, must be subject to some degree of uncertainty,
so that complete scientific advice will include some indication of the
degree of uncertainty involved. The nature of the uncertainties is such
that statistical presentation of confidence limits, etc., are generally not
relevant, and the statement has to bc to some degree subjective,
including judgments on such things as whether a particular mathematical model is applicable to a given situation. The important question
is whether the relative advantages of different regulations (or no
regulation) will be changed. For example, calculations may show that
in a certain trawl fishery an increase in mesh size will result in an
immediate drop in catch in the first year of 5 2 % , followed by an
increase %Tithin three to four years to a level 4.7% above the original
level (i.c. regarding the small fish released as an investment, they will
nearly as a group double in weight). In fact, they may rather more
than double, making the gain perhaps S%, or the gain may be only
4%, but in any event the larger mesh will give a small gain, and advice
in that form can be given t o the regulatory body.
Another form of uncertainty is that many stocks fluctuate for
reasons quite independent of fishery, e.g. due to variation in year-class
strength (Hjort, 1914). In such fisheries the predictions made are
generally not of the actual catch in the future, but are comparisons of the
catch that would be taken if the proposed regulations were introduced,
with the catch taken if different regulations, or if none, were in force.
Proper management, therefore, requires good scientific knowledge
based on adequate data. They are essential for all stocks, not merely
those in immediate need of regulation, since one aspect of proper
management is to avoid unnecessary restrictions, and to be sure
of this requires a certain minimum supply of data. More important,
the proper understanding of a heavily exploited stock depends on
the comparison of the characteristics of the stocks (abundance, as
measured, say, by catch per unit effort, the proportions of different
ages and sizes, etc.) under heavy and light fishing, and therefore
requires adequate information from the period when fishing was
still light.
Though in any fishery a stage could be reached when the possible
benefits from improved management based on better scientific information will be less than the additional costs of getting that information,