Overfishing

Overfishing is, in the simplest terms, the harvest of more fish from a population than it can bear. Yet, the word takes on multiple meanings in practice [Page 1312]and the causes and consequences of, and alternatives to, overfishing are even more complicated.

At a first level of approximation, two kinds of overfishing are possible. Recruitment overfishing refers to the harvest of a species such that its ability to reproduce itself back to its preharvest condition is compromised. This can take the form of destroying broodstock directly or harvesting organisms before they have a chance to reproduce at all. Recruitment overfishing can result in less catches over time and, if sufficiently serious, to crashes in abundance, but this can be temporarily masked by the delay of several years between the culling of one year's breeding population and the resulting hole in the population from the loss of recruitment.

Growth overfishing refers to the taking of fish before they have achieved a size or value determined to be optimal. As a primarily economic issue, it does not bear the same seriousness to the ecology of fisheries, but intense growth overfishing can easily shade into recruitment by harvesting juvenile individuals before they have spawned. The calculation of growth overfishing is contingent on the relationship between natural and fishery mortality, such that the maximum size possible for a given species is seldom achieved in the wild, making harvest of a considerably smaller size perhaps the most remunerative option for fishers.

The decline of a fishery stock may lead to intensified effort to harvest remaining individuals from it, exacerbating overfishing; or it may lead to the abandonment of fishing for other livelihoods.

The consequences of overfishing can be quite severe. Overfished populations can take much longer to rebuild to a healthy condition than it took to degrade them, even if fishing pressure on them is relieved. This can be due to the small number of surviving spawning adults, but can also be because opportunistic species have taken over the habitat. Fishing capacity going unused reduces employment, [Page 1313]creates a crisis of fixed capital investment, contributes to local and regional economic decline, and can—for fisheries crucial to regional food security—contribute to malnutrition. Overfishing in West Africa is believed to contribute to the intensification of the bushmeat trade, which threatens many kinds of wildlife in the region. The decline of a fishery stock may lead to intensified effort to harvest remaining individuals from it, exacerbating overfishing; or it may lead to diversification of effort onto other fisheries (with benign or harmful effects), or the abandonment of fishing for other livelihoods. The specific social, economic, and ecological contexts of a given fishery are important in understanding what a fishery will do when faced with overfishing.

Theories to explain overfishing often converge around the Tragedy of the Commons, which argues common property resources inevitably lead to overexploitation and conflict requiring coercive enforcement and enclosure. This general perspective translated into fisheries implies that with open access situations, where there are no restrictions to harvesting, more fishers will add their effort to the collective effort because their individual gain is larger than the collective loss of that share of the resource, until expenses equal benefits and no profits are gained by anyone.

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