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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 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 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, 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.
The generally employed rubric for managing fisheries to avoid commons tragedies is known as bioeconomics, which seeks to establish and regulate the amounts and types of harvest acceptable to sustain fish populations and the profitability of fisheries. Managers use statistical models drawing on data from research vessels or surveys of commercial landings to model the population dynamics of individual species or multiple species interactions. Surplus production models are utilized to understand how much fishing mortality can be sustained by a population and what biomass will generate the highest rate of increase to augment production. These models are used for establishing Maximum Sustainable Yield (MSY), the largest harvest possible that should leave enough individuals to reproduce an equivalent harvest. Yield per recruit models are used to calculate the best harvest size to maximize catches so as to avoid growth or recruitment overfishing.
Managers make use of the conclusions of these statistical tools through a variety of regulations. Basic management measures include setting Total Allowable Catches, limiting entry to fisheries, mandating size and number limitations on catches, controlling fishers’ access to certain territories or at certain times, or regulating the use of certain types of fishing gears. Drawing on the ideas of Hardin and others, advocates for fishery rationalization support the implementation of Individual Fishing Quotas (IFQs) to simulate private property rights on the premise that marketizing access will lead to better stewardship and allocation of fisheries, reducing overcapitalization.
Pioneered in New Zealand and now used in some Alaskan fisheries, IFQs can reduce wasteful fishing practices caused by “derby fishing,” where a fleet quota is established and fishers compete to bring in the most fish before the quota is filled. They have, however, a tendency to encourage high grading, where fishers throw back suboptimal fish (many of which may die) in order to get the most valuable fish under their IFQ.
Common property theorists pose a counter-narrative to this perspective that stresses that institutions for governing common property, if well-suited to the needs of fish and fishers, can overcome tendencies toward overfishing. Community-based marine resource management is expanding in places like the South Pacific, employing means like conservation education and comanagement by harvesters and the state over defined community territories at sea.
The decline of the groundfish fisheries of Atlantic Canada in the early 1990s is a well-known recent example of overfishing. Many factors contributed to this disaster. More efficient but less selective dragging gear was adopted by a sector of Canadian fishers, which made for more discards. Overcapitalization was encouraged by state support to industrialize the fisheries after the withdrawal of foreign fleets in the late 1970s. A lack of enforcement of fisheries regulations caused more fishers to break rules so as to not lose out on the higher catches that cheating could generate. Overly optimistic projections of fishery populations created false confidence and prevented effective corrective action, and high levels of debt on some vessels mandated that fishers keep fishing or go bankrupt, imposing political economic costs on controlling effort on the fishery.
By contrast, the nearby Maine lobster fishery is considered among the most sustainable fisheries in the world. An informal system of territorial management by fishers gives them incentives for protecting the resource in their areas and disincentives from acting destructively. The gears used are highly selective and allow undersized or egg-bearing lobsters to be returned to the water unharmed. The regulations of the state have evolved over decades to be supported by most fishers because they were seen as beneficial and fair, making compliance rates relatively high. Fisheries like Maine lobster, which have a history of management success, appear to build upon that success, but there is no simple checklist of measures to make the fishery commons less tragic. Careful attention must be paid to the history and contemporary social structure of the fishery as well as its ecology and modifications to it by human action to understand how and why overfishing happens (or does not). One emergent truth is that rules that fishermen feel are counterproductive and unjust do not engender the kind of cooperation that makes management effective, if possible at all.
- Acheson, Capturing the Commons: Devising Institutions to Manage the Maine Lobster Industry (University Press of New England, 2003);
- Jennings et al., Marine Fisheries Ecology (Blackwell Science, 2001);
- Palmer and P. Sinclair, When the Fish Are Gone: Ecological Disaster and Fishers in Northwest New(oundland (Fernwood Publishing, 1997).