The environmental impact of fishing includes issues such as the availability of fish, overfishing, fisheries, and fisheries management; as well as the impact of industrial fishing on other elements of the environment, such as bycatch. These issues are part of marine conservation, and are addressed in fisheries science programs. According to a 2019 FAO report, global production of fish, crustaceans, molluscs and other aquatic animals has continued to grow and reached 172.6 million tonnes in 2017, with an increase of 4.1 percent compared with 2016. There is a growing gap between the supply of fish and demand, due in part to world population growth.

Fishing and pollution from fishing are the largest contributors to the decline in ocean health and water quality. Ghost nets, or nets abandoned in the ocean, are made of plastic and nylon and do not decompose, wreaking extreme havoc on the wildlife and ecosystems they interrupt. Overfishing and destruction of marine ecosystems may have a significant impact on other aspects of the environment such as seabird populations. On top of the overfishing, there is a seafood shortage resulting from the mass amounts of seafood waste, as well as the microplastics that are polluting the seafood consumed by the public. The latter is largely caused by plastic-made fishing gear like drift nets and longlining equipment that are worn down by use, lost or thrown away.

The journal Science published a four-year study in November 2006, which predicted that, at prevailing trends, the world would run out of wild-caught seafood in 2048. The scientists stated that the decline was a result of overfishing, pollution and other environmental factors that were reducing the population of fisheries at the same time as their ecosystems were being annihilated. Many countries, such as Tonga, the United States, Australia and Bahamas, and international management bodies have taken steps to appropriately manage marine resources.

Reefs are also being destroyed by overfishing because of the huge nets that are dragged along the ocean floor while trawling. Many corals are being destroyed and, as a consequence, the ecological niche of many species is at stake. Food and Agriculture Organization (FAO) estimates 30−70% of the waste and by-products generated by fisheries and aquaculture can be transformed for food or non-food usages (e.g. silage, biofuel, fertilizer) or converted into high‐value products (e.g. collagen, gelatin, bioactive peptides, chitin, chitosan). In 2024 the percentage of assessed stocks classified as biologically sustainable by the Food and Agriculture Organization (FAO) declined to 62.4% in 2023, from 64.5% in 2021, with wide differences across regions and species groups.

Effects on marine habitat

Some fishing techniques cause habitat destruction. Blast fishing and cyanide fishing, which are illegal in many places, harm surrounding habitats. Blast fishing refers to the practice of using explosives to capture fish. Cyanide fishing refers to the practice of using cyanide to stun fish for collection. These two practices are commonly used for the aquarium trade and the live fish food trade. These practices are destructive because they impact the habitat that the reef fish live on after the fish have been removed. Bottom trawling, the practice of pulling a fishing net along the sea bottom behind trawlers, removes around 5 to 25% of an area's seabed life on a single run. This method of fishing tends to cause a lot of bycatch. A study of La Fonera Canyon compared trawled versus non-trawled areas. The results show that areas at 500 to 2000 meters depth that is non-trawled have more biodiversity, biomass, and variation of meiofauna than trawled areas at 500 meters depth. Most of the impacts are due to commercial fishing practices. A 2005 report of the UN Millennium Project, commissioned by UN Secretary-General Kofi Annan, recommended the elimination of bottom trawling on the high seas by 2006 to protect seamounts and other ecologically sensitive habitats. This was not done.

In mid-October 2006, United States President George W. Bush joined other world leaders calling for a moratorium on deep-sea trawling. The practice has shown to often have harmful effects on sea habitat and, hence, on fish populations, yet no further action was taken (Vivek). The sea animal's aquatic ecosystem may also collapse due to the destruction of the food chain.

Additionally, ghost fishing is a major threat due to capture fisheries. Ghost fishing occurs when a net, such as a gill net or trawl, is lost or discarded at sea and drifts within the oceans, and can still act to capture marine organisms. According to the Food and Agriculture Organization's 1995 Code of Conduct for Responsible Fisheries, member states should act to minimize the amount of lost and abandoned gear and work to minimize ghost fishing.

Overfishing

Ecological disruption

Overfishing can result in the over-exploitation of marine ecosystem services. Fishing can cause several negative physiological and psychological effects for fish populations including increased stress levels and bodily injuries resulting from lodged fish hooks. Often, when this threshold is crossed, hysteresis may occur within the environment. More specifically, some ecological disturbances observed within the Black Sea marine ecosystem resulted from a combination of overfishing and various other related human activities which adversely affected the marine environment and ecosystem. Ecological disruption can also occur due to the overfishing of critical fish species such as the tilefish and grouper fish, which can be referred to as ecosystem-engineers.

Fishing may disrupt food webs by targeting specific, in-demand species. There might be too much fishing of prey species such as sardines and anchovies, thus reducing the food supply for the predators. Disrupting these types of wasp-waist species may have effects throughout the ecosystem. It may also cause the increase of prey species when the target fishes are predator species, such as salmon and tuna.

Overfishing and pollution of the oceans also affect their carbon storage ability and thus contribute to the climate crisis. Carbon stored in seafloor sediments risk release by bottom-trawling fishing.

Fisheries-induced evolution

Fisheries-induced evolution or evolutionary impact of fishing is the various evolutionary effects of the fishing pressure, such as on size or growth. It is mainly caused by selective fishing on size, bigger fish being more frequently caught. Moreover, policy of minimum landing size, based on the idea that it spares young fishes, have many negative impacts on a population by selecting slow growth individuals.

Bycatch

Bycatch is the portion of the catch that is not the target species. Unintentional bycatch occurs when fishing gear with poor selectivity is used. These are either kept to be sold or discarded. In some instances the discarded portion is known as discards. Even sports fisherman discard a lot of non-target and target fish on the bank while fishing. For every pound of the target species caught, up to 5 pounds of unintended marine species are caught and discarded as bycatch. As many as 40% (63 billion pounds) of fish caught globally every year are discarded, and as many as 650,000 whales, dolphins and seals are killed every year by fishing vessels.

Shark finning and culling

Shark finning is the act of removing fins from sharks and discarding the rest of the shark. The sharks are often still alive when discarded, but without their fins.Spiegel, J. (2000) http://heinonline.org/HOL/LandingPage?handle=hein.journals/bcic24&div=22&id=&page= "Even Jaws deserves to keep his fins: outlawing shark finning throughout global waters". Boston College International and Comparative Law Review, 24 (2): 409–438. Unable to swim effectively, they sink to the bottom of the ocean and die of suffocation or are eaten by other predators. Though studies suggest that 73 million sharks are finned each year,https://www.livescience.com/1027-shark-slaughter-73-million-killed-year.html Shark Slaughter: 73 Million Killed Each Year. Ker Than. September 26, 2006. Retrieved January 1, 2019. scientists have noted that the numbers may actually be higher, with roughly 100 million sharks being killed by finning each year.https://ocean.si.edu/ocean-life/sharks-rays/shark-finning-sharks-turned-prey Ocean.si.edu. Shark finning: Sharks turned prey. Caty Fairclough. Retrieved January 1, 2019. The deaths of millions of sharks has caused catastrophic damage to the marine ecosystem.

Shark culling is the killing of sharks in government-run "shark control" programs.http://www.abc.net.au/news/2013-12-22/can-governments-protect-people-from-killer-sharks/5158880 "Can governments protect people from killer sharks?". ABC News. 2013-12-22. Retrieved January 1, 2019. These programs exist to reduce the risk of shark attacks — however, environmentalists say that they do not reduce the risk of shark attacks; they also say that shark culling harms the marine ecosystem.http://pursuit.unimelb.edu.au/articles/sharks-how-a-cull-could-ruin-an-ecosystem Schetzer, Alana. "Sharks: How a cull could ruin an ecosystem". puruit.unimelb.edu.au. Retrieved January 1, 2019.https://web.archive.org/web/20181002102324/https://www.marineconservation.org.au/pages/shark-culling.html "Shark Culling". marineconservation.org.au. Archived from the original on 2018-10-02. Retrieved January 1, 2019. Shark culling currently occurs in New South Wales, Queensland, KwaZulu-Natal and Réunion.http://www.sharkangels.org/index.php/media/news/157-shark-nets "Shark Nets". sharkangels.org. Archived from the original on 2018-09-19. Retrieved January 1, 2019.https://www.nzherald.co.nz/world/news/article.cfm?c_id=2&objectid=11847758 "Man Who Devoted Life To Sharks, Killed Off The Coast Of Reunion". nzherald.co.nz. April 30, 2017. Retrieved January 1, 2019. Queensland's "shark control" program killed roughly 50,000 sharks between 1962 and 2018 — Queensland's program uses lethal devices such as shark nets and drum lines.https://www.news.com.au/technology/science/animals/aussie-shark-population-is-staggering-decline/news-story/49e910c828b6e2b735d1c68e6b2c956e Aussie shark population in staggering decline. Rhian Deutrom. December 14, 2018. Retrieved January 1, 2018. Thousands of other animals, such as turtles and dolphins, have been killed in Queensland as bycatch.http://www.afd.org.au/news-articles/queenslands-shark-control-program-has-snagged-84000-animals Action for Dolphins. Queensland's Shark Control Program Has Snagged 84,000 Animals. Thom Mitchell. November 20, 2015. Retrieved January 1, 2019. Queensland's shark culling program has been called "outdated, cruel and ineffective".https://www.ntd.tv/2018/09/04/video-endangered-hammerhead-sharks-dead-on-drum-line-in-great-barrier-reef/ Phillips, Jack (September 4, 2018). "Video: Endangered Hammerhead Sharks Dead on Drum Line in Great Barrier Reef". ntd.tv. Retrieved January 1, 2019. The shark culling program in New South Wales (which uses nets) has killed thousands of sharks, turtles, dolphins and whales. KwaZulu-Natal's shark culling program killed more than 33,000 sharks in a 30-year period.

Marine debris