Overfishing

Overfishing is the removal of a species of fish (i.e. fishing) 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 stock), resulting in the species becoming increasingly underpopulated in that area. Overfishing can occur in water bodies of any sizes, such as ponds, wetlands, rivers, lakes or oceans, and can result in resource depletion, reduced biological growth rates and low biomass levels. Sustained overfishing can lead to critical depensation, where the fish population is no longer able to sustain itself. Some forms of overfishing, such as the overfishing of sharks, has led to the upset of entire marine ecosystems.^[1] Types of overfishing include growth overfishing, recruitment overfishing, and ecosystem overfishing.

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.

Since the growth of global fishing enterprises after the 1950s, intensive fishing has spread from a few concentrated areas to encompass nearly all fisheries. The scraping of the ocean floor in bottom dragging is devastating to coral, sponges and other slower-growing benthic species that do not recover quickly, and that provide a habitat for commercial fisheries species. This destruction alters the functioning of the ecosystem and can permanently alter species' composition and biodiversity. Bycatch, the collateral capture of unintended species in the course of fishing, is typically returned to the ocean only to die from injuries or exposure. Bycatch represents about a quarter of all marine catch. In the case of shrimp capture, the bycatch is five times larger than the shrimp caught.

A report by FAO in 2020 stated that "in 2017, 34 percent of the fish stocks of the world's marine fisheries were classified as overfished".^[2]^: 54 Mitigation options include: Government regulation, removal of subsidies, minimizing fishing impact, aquaculture and consumer awareness.

Tuna has been caught by the locals in the upper Adriatic for centuries. Increasing fishing prevented the large schools of from migrating into the Gulf of Trieste. The last major tuna catch was made in 1954 by the fishermen of Santa Croce, Contovello and Barcola.^[18]

little tunny

after overfishing and an El Niño season^[19] largely depleted the Peruvian anchovetas from its waters.^[20]^[21] Anchovies were a major natural resource in Peru; indeed, 1971 alone yielded 10.2 million metric tons of anchovies. However, the following five years saw the Peruvian fleet's catch amount to only about four million tons.^[19] This was a major loss to Peru's economy.

The Peruvian coastal anchovy fisheries crashed in the 1970s

The off Newfoundland,^[22] and the 1992 decision by Canada to impose an indefinite moratorium on the Grand Banks, is a dramatic example of the consequences of overfishing.^[23]

collapse of the Atlantic northwest cod fishery

The fisheries in the Irish Sea, the west English Channel, and other locations have become overfished to the point of virtual collapse, according to the UK government's official Biodiversity Action Plan. The United Kingdom has created elements in this plan to attempt to restore the fishery, but the expanding global human population and the expanding demand for fish has reached a point where demand for food threatens the stability of these fisheries, if not the species' survival.^[24]

sole

Many are at risk, such as orange roughy and sablefish. The deep sea is almost completely dark, near freezing, and has little food. Deep sea fish grow slowly because of limited food, have slow metabolisms, low reproductive rates, and many do not reach breeding maturity for 30 to 40 years. A fillet of orange roughy at the store is probably at least 50 years old. Most deep sea fish are in international waters, where there are no legal protections. Most of these fish are caught by deep trawlers near seamounts, where they congregate for food. Flash freezing allows the trawlers to work for days at a time, and modern fishfinders target the fish with ease.^[25]

deep sea fish

became extinct in the Great Lakes in the 1980s. Until the middle of the 20th century, the walleye was a commercially valuable fish, with about a half million tonnes being landed in the period from about 1880 to the late 1950s, when the populations collapsed, apparently through a combination of overfishing, anthropogenic eutrophication, and competition with introduced rainbow smelt.

Blue walleye

Examples of overfishing exist in areas such as the North Sea, the Grand Banks of Newfoundland and the East China Sea.^[16]^[17] In these locations, overfishing has not only proved disastrous to fish stocks, but also to the fishing communities relying on the harvest. Like other extractive industries such as forestry and hunting, fisheries are susceptible to economic interaction between ownership or stewardship and sustainability, otherwise known as the tragedy of the commons.

Biological overfishing occurs when fishing has reached a level where the stock biomass has negative marginal growth (reduced rate of biomass growth), as indicated by the red area in the figure. (Fish are being taken out of the water so quickly that the replenishment of stock by breeding slows down. If the replenishment continues to diminish for long enough, replenishment will go into reverse and the population will decrease.)^[40]

mortality

Economic or bioeconomic overfishing additionally considers the cost of fishing when determining acceptable catches. Under this framework, a fishery is considered to be overfished when catches exceed where resource rent is at its maximum. Fish are being removed from the fishery so quickly that the profitability of the fishery is sub-optimal. A more dynamic definition of economic overfishing also considers the present value of the fishery using a relevant discount rate to maximise the flow of resource rent over all future catches.

maximum economic yield

Article 61 requires all coastal states to ensure that the maintenance of living resources in their is not endangered by over-exploitation. The same article addresses the maintenance or restoration of populations of species above levels at which their reproduction may become seriously threatened.

exclusive economic zones

Article 62 provides that coastal states: "shall promote the objective of optimum utilization of the living resources in the exclusive economic zone without prejudice to Article 61"

Article 65 provides generally for the rights of, inter alia, coastal states to prohibit, limit, or regulate the exploitation of marine mammals.

Williams, Robyn (13 February 2021). . The Science Show. Australian Broadcasting Corporation.