Perhaps the most obvious shortcoming of a purely ecological approach is its failure to recognize that the exploitation of a natural resource is usually a business enterprise, in which the value of the harvest must be set against the costs of obtaining that harvest. Even if we distance ourselves from any preoccupation with 'profit', it makes no sense to struggle to obtain the last few tonnes of an MSY if the money spent in doing so could be much more effectively invested in some other means of food production. The basic idea is illustrated in Figure 15.15. We seek to maximize not total yield but net value - the difference between the gross value of the harvest and the sum of the fixed costs (interest payments on ships or factories, insurance, etc.) and the variable costs, which increase with harvesting effort (fuel, crew's expenses, etc.). This immediately suggests that the economically optimum yield (EOY) is less than the MSY, and is obtained through a smaller effort or quota. However, the difference between the EOY and the MSY is least in enterprises where most costs are fixed (the 'total cost' line is virtually flat). This is especially the case in high investment, highly technological operations such as deep-sea fisheries, which are therefore most prone to overfishing even with management aimed at economic optima.
A second important economic consideration concerns 'discounting'. This refers to the fact that in economic terms, each bird in the hand now (or each fish in the hold) is worth more than an equivalent bird or fish some time in the future. The reason is basically that the value of the current catch can be placed in the bank to accrue interest, so that its total value increases. In fact, a commonly used discount rate for natural resources is 10% per annum (90 fish now are as valuable as 100 fish in 1 year's time) despite the fact that the difference between the interest rates in the banks and the rate of inflation is usually only 2-5%. The economists' justification for this is a desire to incorporate 'risk'. A fish caught now has already been caught; one still in the water might or might not be caught - a bird in the hand really is worth two in the bush.
On the other hand, the caught fish is dead, whereas the fish still in the water can grow and breed (although it may also die). In a very real sense, therefore, each uncaught fish will be worth more than 'one fish' in the future. In particular, if the stock left in the water grows faster than the discount rate, as is commonly the case, then a fish put on deposit in the bank is not so sound an investment as a fish left on deposit in the sea. Nevertheless, even in cases like this, discounting provides an economic argument for taking larger harvests from a stock than would otherwise be desirable.
Moreover, in cases where the stock is less productive than the discount rate - for example, many whales and a number of long-lived fish - it seems to make sense, in purely economic terms, not only to overfish the stock, but actually to catch every fish ('liquidate the stock'). The reasons for not doing so are partly ethical - it would clearly be ecologically short sighted and a disdainful way of treating the hungry mouths to be fed in the future. But there are also practical reasons: jobs must be found for those previously employed in the fishery (or their families otherwise provided for), alternative sources of food must be found, and so on. This emphasizes, first, that a 'new economics' must be forged in which value is assigned not only to things that can be bought and sold - like fish and boats - but also to more abstract entities, like the continued existence of whales or other 'flagship species' (Hughey et al., 2002). It also stresses the danger of an economic perspective that is too narrowly focused. The profitability of a fishery cannot sensibly be isolated from the implications that the management of the fishery has in a wider sphere.
'Social' factors enter in two rather separate ways into plans for the man- social repercussions agement of natural resources. First, practical politics might dictate, for instance, that a large fleet of small, individually inefficient boats is maintained in an area where there are no alternative means of employment. In addition, though, and of much more widespread importance, it is necessary for management plans to take full account of the way fishermen and harvesters will behave and respond to changing circumstances, rather than assuming that they will simply conform to the requirements for achieving either ecological or economic optima. Harvesting involves a predator-prey interaction: it makes no sense to base plans on the dynamics of the prey alone whilst simply ignoring those of the predator (us!).
the economically optimum yield -typically less than the MSY
discounting: liquidating stocks, or leaving them to grow?
600 800 1000 1200 1400 Herd size
Figure 15.16 The fleet size of the North Pacific fur seal fishery (predators) responded to the size of the seal herd (prey) between 1882 and 1900 by exhibiting an anticlockwise predator-prey spiral. (After Hilborn & Walters, 1992; from data of Wilen, 1976, unpublished observations.)
The idea of the harvester as predator is reinforced in Figure 15.16, which shows a classic anticlockwise predator-prey spiral (see Chapter 10) for the North Pacific fur seal fishery in the last years of the 19th century. The figure illustrates a numerical response on the part of the predator - extra vessels enter the fleet when the stock is abundant, but leave when it is poor. But the figure also illustrates the inevitable time lag in this response. Thus, whatever a modeler or manager might propose, there is unlikely ever to be some perfect match, at an equilibrium, between stock size and effort. Moreover, whilst the sealers in the figure left the fishery as quickly as they had entered it, this is by no means a general rule. The sealers were able to switch to fishing for halibut, but such switches are often not easy to achieve, especially where there has been heavy investment in equipment or longstanding traditions are involved. As Hilborn and Walters (1992) put it, 'Principle: the hardest thing to do in fisheries management is reduce fishing pressure'.
Switching is one aspect of a harvester's predatory behavior - its functional response (see Chapter 10). Harvesters will also generally 'learn' as there is an inevitable trend towards technological improvement. Even without this, harvesters usually improve their efficiency as they learn more about their stock -notwithstanding the assumptions of simple fixed-effort models.
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