Binding legislation and harvest management strategies... are urgently needed to address the disproportionate impact of fisheries on cartilaginous fishes.
– IUCN global study 2010
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Binding legislation and harvest management strategies... are urgently needed to address the disproportionate impact of fisheries on cartilaginous fishes.
Threatened sharks are those vulnerable to endangerment (extinction) in the near future. The International Union for Conservation of Nature (IUCN) is the world's oldest global environmental organization. It evaluates threatened species, and treats threatened species not as a single category, but as a group of three categories, depending on the degree to which they are threatened:
The term threatened strictly refers to these three categories (critically endangered, endangered and vulnerable), while vulnerable is used to refer to the least at risk of these categories. The terms can be used somewhat interchangeably, as all vulnerable species are threatened, all endangered species are vulnerable and threatened, and all critically endangered species are endangered, vulnerable and threatened. Threatened species are also referred to as a red-listed species, as they are listed in the IUCN Red List of Threatened Species.
Overfishing is the removal of aquatic animals — primarily fish — from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing fish stocks), resulting in the species becoming increasingly underpopulated in that area. Excessive fishing practices can occur in water bodies of any sizes, from ponds, wetlands, rivers, lakes to seas and oceans, and can result in resource depletion, reduced biological growth rates and low biomass levels. Sustained overfishing, especially industrial-scale commercial fishing, can lead to critical depensation, where the fish population is no longer able to sustain itself, resulting in extirpation or even extinction of species. Some forms of overfishing, such as the overfishing of sharks, has led to the upset of entire marine ecosystems. Types of overfishing include growth overfishing, recruitment overfishing, and ecosystem overfishing. Overfishing not only causes negative impacts on biodiversity and ecosystem functioning, but also reduces fish production, which subsequently leads to negative social and economic consequences.
The ability of a fishery to recover from overfishing depends on whether its overall carrying capacity and the variety of ecological conditions are suitable for the recovery. Dramatic changes in species composition can result in an ecosystem shift, where other equilibrium energy flows involve species compositions different from those that had been present before the depletion of the original fish stock. For example, once trout have been overfished, carp might exploit the change in competitive equilibria and take over in a way that makes it impossible for the trout to re-establish a breeding population.