Direct experience in many fisheries, confirmed by theoretical studies, has shown the serious effects that uncontrolled fishing can have on fish stocks, and on the fisheries based on them. The scientific studies have shown the value of proper management and regulation, and that management measures can he divided into those controlling the total amount of fishing, and those affecting the size or other characteristics of the fish caught (e.g. size limits, minimum mesh sizes of trawls, etc.). This note is only concerned with the first of these.
The biological consequences of control of the amount of fishing have been well described in a number of papers (Beverton and Holt 1957, Schaefer 1954) and do not need repeating in detail. However, although it has been the common experience of bodies concerned with fisheries management that the practical and economic consequences of measures taken to limit the amount of fishing have often been much less beneficial than the simple biological analysis would predict, few studies have been made of practical difficulties of limiting fishing. Some of the more obvious problems, e.g. of a greatly shortened season with a single quota system have of course become widely appreciated.
The biological reasons for wishing to control fishing can be directly shown by a simple curve relating the amount of fishing, strictly the fishing mortality coefficient, to the average long-term catch taken by that fishing mortality. The precise form of this curve will vary with the stock of fish concerned, and with adjustments that may be made to the composition of the catch (e.g. by mesh regulation), but it will generally lie between the two extremes shown in Figure 1 - (a) a curve with a pronounced maximum, and a sharp fall for rates of fishing beyond the maximum, and (b) a curve which tends to flatten out, but still rises, if only very slowly, for quite high fishing rates, and has no clear maximum.
For fisheries with a type (a) yield curve there can be large benefits if the stock is over-fished (e.g. at point A) by restricting fishing and thus increasing the catch: these benefits will occur whether or not the reduction of the amount of fishing allows a reduction in the costs of fishing. In type (b) curves there can be no increase in catch, but there may still be benefits, possibly considerable, if costs can be reduced.
The potential benefits may be seen more clearly if, taking a more representative curve, such as (c) in Figure 1, the fishing mortality is expressed in terms of the cost of fishing, and the catch in value. To a first approximation, if nothing is done to affect the efficiency of fishing operations, total costs will be proportional to the fishing mortality, and the value of the catch to the total weight. This latter assumption ignores, inter alia, the fact that with increased mortality the average size, and hence often the price per kg, will be lower. Also with fewer age-groups present in the catch, year-to-year fluctuations due to year-class variations will be more pronounced which may also tend to reduce the value of a given average annual catch. The assumption is also implicitly made that the elasticity of demand is unity, but since an increasing proportion of fishery products are being supplied to a comprehensive world-wide market (fish meal, shrimps, frozen fish sticks, etc.), changes in the supply from a single stock can make little difference to the price.
A curve relating costs to value, such as Figure 2, can then be derived. Also shown in Figure 2, is the line of equal costs and value. In the absence of regulation fishing will tend to stabilize at the point P where the line outs the curve.1/ If in the example of Figure 2, fishing is reduced to give the maximum catch, point Q, then there will be some benefit from the increased catch (QX), but there will also be a benefit (PX) from reduced costs - provided the efficiency is not altered. Often, as in the figure, this benefit can be greater than that from increased catch. Also, if the fishing is further reduced, say to R, then the further reduction in costs (RY) is possible which will be considerably greater than the reduction in value (QY). For fixed economic conditions a point giving the maximum net economic return (value less costs) can be defined. Since economic conditions do vary this point is not absolutely fixed, and cannot be used as the uniquely definable objective of fishery management in place of the objective of maximum physical yield which also has both biological and economic shortcomings (Gulland 1968). However it will always be true that in all situations (with a few trivial exceptions) it is desirable on economic grounds to fish at less than the rate giving the maximum physical yield.
1/ This may be an optimistic view. Many fisheries are now developing very rapidly. Since the stocks may take some time to react to increased fishing, and investment policy is commonly based on past catch rates (at possibly much larger stocks), the fishing effort (in terms of fleet size, etc.) can easily overshoot the equilibrium position and take a long time to return.
FIG. 1
FIG. 2
The close interrelation between biology and economics, and the economic implications of the presence or absence of regulations, using the same or similar arguments to those above, has been recognized by biologists for at least 30 years (Graham 1935, Beverton 1953) and have more recently been forcibly pointed out by a number of economists (Crutchfield 1959, Gordon 1954, Scott 1955).
The full benefits of regulating the amount of fishing therefore require the satisfaction of two conditions - reduction of the fishing mortality coefficient, F, to the desired level, and ensuring that this reduction of F is achieved with the minimum loss in the efficiency of the fishing operations.
The preceding analysis assumes that the only variable factor affecting the fish stocks is the amount of fishing, but other, environmental, factors can have big effects. One of these is the variation in recruitment, the number of young fish reaching commercial sizes. The strength of year-classes (the numbers in each annual brood) can vary greatly and the causes of these variations are not clearly understood. For this reason (among others) scientific assessments are often presented in terms of the yield per recruit; usually the yield per recruit from a given fishing mortality is less effected by environmental factors than is the yield.
These natural fluctuations cause the desirable catch (on almost any criterion) to vary from year to year, but the desirable fishing mortality e.g. that giving the maximum long-term yield in weight, is more constant. However, a fishing mortality which is the optimum when year-class strengths are average may be too high when weak year-classes are present in the fishery, since it may result in too low a spawning stock; it may therefore be necessary to reduce the fishing mortality when year-classes are poor, and possibly to increase it when good year - classes are present. This agrees with economic considerations - it is worthwhile to incur extra costs to get a bit nearer the maximum physical yield when this yield is large. This effect is in addition to the increase in total yield which will occur, even for a fixed fishing mortality, when a good year-class occurs, and which may require a bigger vessel or shore capacity to handle it.
