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Overfishing

Overfishing

BIBLIOGRAPHY

Overfishing occurs when the stock (biomass ) of a fish species has been subjected to a rate or level of fishing mortality (usually from commercial fishing) that has reduced it below its capacity to maintain an established fishing (harvest ) yield. This yield is usually specified as the maximum sustainable yield (MSY), defined as the maximum amount of fish that can be removed from the biomass on a sustained basis while maintaining the same stock level, given the stocks biological growth function (dynamics ). Overfishing is inherently a biological concept, although it is fundamentally tied to economic behavior because it involves fishing pressure or intensity beyond an optimum level. The model used to evaluate it is thus called a bioeconomic model.

To more specifically define overfishing it is necessary to determine what fishing level would be optimal in terms of the biological stock, or not constitute overfishing. The first step is to define the biological growth function, which is generally attributed to Milner B. Schaefer (1954; see also Anderson 1986). Given his assumption of a logistic growth equation, a sustainable yield curve can be drawn as a parabola, expressed in terms of either the biomass stock (S) or fishing effort (E), as shown on the left and right hand side of Figure 1, respectively.

In an unexploited state (no mortality from fishing) the fishery is in a biological equilibrium where growth is zero, at the left-hand extreme of both curves in the figure. If fishing then begins, defined in terms of increasing fishing effort (days, or boat/crew), the fish stock falls (a movement to the right on the horizontal axis in both panels). The biomass (fish) growth that may be harvested (caught) on a sustainable basis rises, however (as indicated by the increasing yield on the vertical axis with a move up the

curves), because the stock will be regenerating toward the biological equilibrium.

The maximum possible sustained yield is attained at the very top of the curve(s), which shows the MSY fish stock (Smsy), the effort required to harvest that stock on a sustained basis if no shock changes the curves (Emsy), and the maximum catch attainable in that state (Cmsy). If more fishing effort than Emsy is applied to harvesting, however, the stock and thus sustainable catch decline (a movement down the right hand sides of the curves), because reproduction is not proceeding fast enough to counteract the exploitation. This is a state of overfishing, represented by the lower sustained yield (or mortality) than possible (such as at C < Cmsy). The stock is thus overfished, characterized by a lower stock than at the MSY point (S < Smsy), and the fishery is overcapitalized (E > Emsy).

Overfishing is the likely outcome in an unmanaged fishery because it is common property or open access (no one owns the fish), so fishers will keep fishing as long as they find it profitable. Such overuse is generally expected for common property or common pool resources, a problem often called the tragedy of the commons (see Hardin 1968). That is, overexploitation of the stock occurs because without property rights fishing will continue until the average rather than marginal benefits of harvesting are equal to marginal costs. In the standard bioeconomic model this results in an effort level on the right hand side of effort curve.

A primary goal of fishing management is thus to counteract the incentive to fish the stock down to an over-exploited or overfished state. This can be accomplished by command and control polices such as limits on the total allowable catch or days at sea. Such policies still do not provide incentives for fishers to maximize the economic value of the fishery, which is best accomplished by conferring property rights on fishers to approximate a socially optimal outcome. Such programs can be difficult to implement, however, due to distributional and political issues about who is allowed to fish, how much revenue each fisher receives, and how such rights should be conferred (e.g., for free or auctioned off with the proceeds going to the public or to support fishery management).

SEE ALSO Coase Theorem; Externality; Tragedy of the Commons

BIBLIOGRAPHY

Anderson, Lee. 1986. The Economics of Fisheries Management. Baltimore, MD: Johns Hopkins University Press.

Hardin, Garrett. 1968. The Tragedy of the Commons. Science 162: 12431248.

Schaefer, Milner B. 1954. Some Aspects of the Dynamics of Populations Important to the Management of Commercial Marine Fisheries. Bulletin of the Inter-American Tropical Tuna Commission 1: 2556.

Catherine J. Morrison Paul

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overfishing

overfishing Practice of catching too many marine creatures for an ecological balance to be maintained, resulting in the severe reduction in, or even disappearance of, food fishes, whales and other marine animals. It has become a worldwide concern, with falling catches in most of the world's major fisheries. It remains an international problem largely because of the inability of marine law to regulate fishing and whaling.

http://www.oceanconservancy.org; http://www.nmfs.noaa.gov; http://www.panda.org

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