Overfishing

Overfishing is the removal of aquatic animals from a body of water at a rate faster than the species can naturally replenish itself. This process involves the overexploitation of existing fish stocks. When this happens, the species becomes increasingly underpopulated in that specific area. Overfishing can occur in many environments, including ponds, rivers, lakes, and oceans. It can lead to resource depletion and lower biomass levels. If industrial-scale commercial fishing continues, it can cause critical depensation. This is a state where the population can no longer sustain itself. This often results in extirpation or even extinction.

Scientists recognize three distinct types of biological overfishing. The first is growth overfishing. This occurs when fish are harvested at an average size smaller than the size needed to produce the maximum yield per recruit. A recruit is an individual that reaches maturity or specific fishery limits. The second type is recruitment overfishing. This happens when the spawning biomass, or the mature adult population, is depleted too much. At this level, there are not enough adults to produce enough offspring to replenish the group. The third type is ecosystem overfishing. This occurs when the balance of the entire ecosystem is altered. For example, removing large predatory species can cause an increase in small forage fish.

Overfishing can also trigger a process called fishing down the food web. This occurs when all the larger fish in an area are caught. Fishermen then begin to target smaller individuals to meet demand. This process decreases fish populations and reduces genetic diversity. Lower genetic diversity makes species more susceptible to disease and less able to adapt to environmental stressors. Additionally, catching smaller fish leads to the breeding of smaller offspring. This is problematic because smaller female fish are often less fecund, meaning they produce fewer eggs. This cycle makes it much harder for the population to recover.

History shows that intensive fishing has expanded significantly since the 1950s. Before this time, fishing was mostly concentrated in a few specific areas. Now, intensive fishing has spread to encompass nearly all fisheries globally. However, significant overfishing was even observed in pre-industrial times. The western Atlantic Ocean saw heavy fishing starting during early European colonization. Data from the FAO shows a clear downward trend in sustainable fishing. In 1974, 90% of fish stocks were at biologically sustainable levels. By 2015, that number dropped to only 66.9%.

In contrast, the percentage of fish stocks at unsustainable levels has grown. In 1974, only 10% of stocks were fished at unsustainable levels. By 2015, this figure rose to 33.1%. The largest increases in these unsustainable levels occurred during the late 1970s and 1980s. Certain regions show much higher rates of overfishing than others. In 2015, the Mediterranean and Black Sea had the highest percentage of unsustainable stocks at 62.2%. The Southeast Pacific followed closely at 61.5%. The Eastern Central Pacific and Northwest Pacific had much lower proportions, ranging from 13% to 17%.

Specific examples highlight the severe consequences of these trends. In the 1970s, the Peruvian anchovy fishery crashed due to overfishing and El Niño. The catch fell from 10.2 million metric tons in 1971 to about four million tons over the next five years. This caused a major loss to the economy of Peru. Another example is the Atlantic northwest cod fishery off Newfoundland. This collapse led Canada to impose an indefinite moratorium in 1992. Deep-sea fish like the orange roughy are also at high risk. These fish grow very slowly and may not reach breeding maturity for 30 to 40 years.

Overfishing also causes significant collateral damage through bycatch. Bycatch is the accidental capture of unintended species during fishing. This represents about a quarter of all marine catch. In shrimp fishing, the mass of bycatch can be five times larger than the shrimp caught. Many of these animals die from injuries or exposure after being returned to the water. Furthermore, methods like bottom dragging can scrape the ocean floor. This destroys coral, sponges, and other slow-growing benthic species. These species provide vital habitats for commercial fish.

Addressing these issues requires various mitigation options. Governments can use regulation and the removal of subsidies to control fishing. Minimizing fishing impact and using aquaculture are also important strategies. Consumer awareness can also play a role in protecting global fish stocks. Protecting these systems is vital because overfishing threatens the food supply for millions of people. It also impacts biodiversity and the stability of entire marine ecosystems.