Overfishing is taking out of the sea more than natural population growth can sustain. Overfishing has a number of causes, the most ruthless being "chronic overcapacity" of modern fishing fleets to effectively take far more fish than can be replaced.
The global marine fish catch almost doubled between 1975 and 1995, and the state of the world's fisheries in 1999 reached crisis point. In 1995 the international community responded by creating the the UN Food and Agricultural Organisation Code of Conduct for Responsible Fisheries.
The move to even more destructive deep-water fishing is being encouraged by governments who are offering subsidies to alleviate the hardship that has been brought on by the collapse of shallow-water fish stocks. Forty percent of the world's trawling grounds are now waters that are deeper than the edge of the continental shelves.
Fishermen, nations and international bodies are reluctant to limit catches. In some circumstances, a fishery will be more profitable by catching every fish possible and investing the proceeds. When catches are limited, the form of limitation may encourage overfishing some species. When whale quotas were set in Blue Whale Units — one BWU is equivalent to two fin whales, two and a half humpbacks and six Sei whales – it was more profitable to take a blue whale whenever it showed up even when the whaler was seeking smaller species. The difficulty of negotiating international conservation legislation makes the process of limiting overfishing drawn out, sometimes to the point of endangering species.
Researchers say that only comprehensive action can save the world's great fisheries from complete collapse (the worst situation being the North Atlantic region). They urge the immediate introduction of marine reserves, cuts in fishing fleets and the abandonment of subsidies (in 2001 around $2.5bn a year for the North Atlantic region alone).
In 2014, the World Wildlife Fund (WWF) reported 53% exploitation of global fisheries and a further 32% over-exploited, depleted or recovering from depletion.
Until its maximum of 100 million tonnes in 1989, fish catches had grown annually, doubling since 1963 and with a five-fold increase since 1950. Since 1989, the world fish catch has remained at about 97 million tonnes. Although the global catch is now recognized as having been declining in recent years, earlier increases in tonnages are now known to have masked a shift from valuable species to much less edible ones. There has also been a trend for the developing country share to be reduced (for example from 52.7% in 1986 to 51.5% in 1987; the reduction was mostly attributed to lower catches of small pelagic fish in the south-eastern Pacific, which had been responsible for an increase in 1986). In 1993 FAO reported 13 of the 17 major fishing global fisheries were depleted or in serious decline. The other four were already overexploited.
In the North Atlantic Ocean region, fish numbers in 2000 were just one sixth of what they were in 1900. This situation was even worse than earlier predictions had anticipated. The crisis was evident in the collapse in catches. For prime table-fish, catches were down from 9 kg per person in the 1960s to around 3 kg per person in 2000. That trend extrapolated means that by 2010 most fish will have effectively disappeared from the market.
The shortage in the North Atlantic has had impacts elsewhere, as more and more fish were imported into Western Europe and North America from other parts of the world, effectively "hiding the crisis" from their consumers. For instance, Information up to late 1988 showed that Latin American fish production went down to the 1985 level of 13.7 million tonnes, after the 1986 peak of 16 million tonnes; with Chile, Ecuador and Peru having suffered decreases of 14, 41 and 23% respectively.
The catch has collapsed for 9 of the 12 Atlantic groundfish stocks. The take of the more edible species such as cod, haddock and flounder has decreased by over 75%. Pacific salmon and western Atlantic bluefin tuna are nearing biological extinction. North Atlantic's cod stocks have collapsed from an estimated spawning stock of 264,000 tonnes in 1970 to under 60,000 in 1995. Taking of juveniles of the North Atlantic swordfish cut populations by 70 percent. Most of the commercial fishing areas in the coastal waters of the USA are in difficulty with the decimation of species after species. After 350 years of continuous fishing the Georges Bank area, the oldest fishing area in the USA, was stripped bare in a decade and is now largely closed to fishing. The cod population in Canada's Grand Banks also collapsed with the spawning stock reduced from 1.6 million to 22,000.
In 1996, for nearly half of stocks fished around the UK, by the UK and other international fleets, the spawning population was estimated to be at a level where there is a risk of stock collapse. Plaice stocks in the North Sea in 1996 were 49 per cent less than at their peak in 1986. Stocks of cod in 1996 were at half the levels seen in the early 1980s.
Despite successive cuts in the EEC/EU catch allowances, the spawning stock of North Sea cod in 1990 was less than 80,000 tonnes, compared with 168,000 tones in 1982. Haddock stocks fell from 285,000 tonnes to 80,000 tonnes in the same period. In 1992, the EEC/EU has decided to reduce its fishing fleet by at least 20%. Together with Canada it has suspended cod fishing of Canadian coasts, and Iceland has restricted its cod catch to 40% less, even though cod has accounted for around a third of all Icelandic exports. In order to enforce quotas, Namibia has banned foreign boats from its waters and Sierra Leone has partially followed suit. The South Pacific Forum Fisheries Agency, made up of eight island nations, has restricted Asian and USA fishing vessels to 200 boats, against angry complaints.
Previous (and in some cases ongoing) disputes over fishing rights included: the US and China over the UN driftnet ban; Ecuador, between the developing national fishing industry and small scale traditional fishermen; the Caribbean with illegal fishing by Japan, Russia, Taiwan, US and Venezuela; the Patagonian Shelf, with illegal fishing by Taiwanese and South Korean fleets; US and France over bluefin tuna; the Bay of Biscay, with British, French and Spanish fishermen in dispute over tuna catches; Iceland and Norway in dispute over Arctic fishing rights; China and Vietnam over illegal fishing; Japan and Russia over national waters, and Russia, US, China, Japan and South Korea over illegal operations in the Bering Sea.