Marine Fisheries

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Marine Fisheries


Around half of the world’s fish species are found in the marine environment, and those that are edible have long provided an important food resource for humans and other animals. Fishing is now a huge commercial operation and marine fisheries have grown in size and sophistication in the last 50 years. Fish are caught in nets or on lines, sorted on board a fishing vessel, and then brought back to shore.

Although the oceans are vast, their fish stocks are not limitless. Many marine fisheries are now taking fish faster than stocks can renew themselves. This means that some fishes, such as the Atlantic cod, are now regarded as endangered species and several marine ecosystems are under threat. Therefore, many nations have now put limits on fishing, although it is not known to what extent fish stocks can recover. Consumers can help by purchasing from sustainable marine fisheries, which catch only those species whose populations are not threatened.

Historical Background and Scientific Foundations

There is a long tradition of fishing, both for pleasure and for food, around the world. Fish are highly valued as a source of animal protein, comparing favorably with meat in terms of cost and health benefits. Many health authorities actively promote regular consumption of fish, such as salmon and sardines, that are rich in heart-healthy omega-3 fatty acids. The average consumption of fish worldwide is about 30 pounds a week. Fishing covers harvesting fish themselves, shellfish, and other aquatic animals, such as squid and octopus, but not whales. Some marine fish are farmed in tanks, rather than in the open water. Besides food, fish are used for their oils, enzymes, and other manufactured products, as well as having a decorative and educational function in aquaria.

Of the 30,000 or so of identified fish species, about 500 are known to be edible. Around half of all known fish species live in a marine environment; the rest are found in freshwater. Tuna is found in the open ocean, whitefish and salmon around temperate coastlines, shrimp in coastal seas and oysters, clams, and mussels in estuaries. There are also areas called upwellings, where nutrient-rich deep water comes to the surface and can support high fish productivity. These are found off the western coasts of Africa, North and South America, across the Western Pacific, and around the Southern Ocean and are a popular site for marine fisheries. Countries with major fish industries include China, the United States, Chile, Iceland, and Norway.

Because the seas and oceans are so large, covering 70% of Earth’s surface, it was once assumed that the supply of marine organisms to meet human needs is limitless. The fishing industry therefore expanded dramatically from the 1960s, with more vessels being put to sea and advances in fishing technology bringing in higher yields of fish. The way fish are caught varies with the size of the operation and the type of fish involved. Most fishing involves pots, lines, and nets, but the size of the vessel may vary from a single fisher with a few lines to massive ocean-going trawlers casting thousands of square miles of strong plastic netting each day. Fish harvesting has increased 5 fold in the last 50 years. From 1970 to 1990, it went up from 60 million to 80 million tons per year and then leveled off. Fish now account for about 16% of animal protein consumption by humans, and the industry employs about 10 million people directly, with many millions more being dependent on it for sustenance.

Removal of large numbers of fish species cause shifts in the marine food web. There are other effects on the marine ecosystem. Fishers divide their catch into two groups. Undersized and diseased fish that will not sell are thrown back to avoid taking up valuable space on the fishing vessel. The keepers, as they are known, are taken back to shore. The discards provide a food source for large sea birds, like the great skua in the North Sea. However, fewer of these discards have been available in recent years, because fish hauls have been restricted. Great skua populations have declined and those birds remaining have had to turn to alternative food sources, such as other, smaller, sea birds.

Impacts and Issues

The unsustainable approach of marine fisheries over the last 50 years or so has now hit fish stocks hard. The marine environment can support the taking of around 100 million tons of fish a year. The global fishing fleet is now about two and a half times larger than what the oceans can sustainably support. Motors have replaced sails, boats are bigger, and onboard refrigerators allow fishers to stay at sea longer. Fisheries are sometimes sub-


FOOD WEB: An interconnected set of all the food chains in the same ecosystem.

OVERFISHING: Overharvesting applied to fish.

OVERHARVESTING: Harvesting so much of a resource that its economic value declines and/or its existence is threatened.

SUSTAINABLE: Capable of being sustained or continued for an indefinite period without exhausting necessary resources or otherwise self-destructing: often applied to human activities such as farming, energy generation, or the maintenance of a society as a whole.

sidized unfairly and may be allowed to encroach upon the waters of developing nations, who have a more urgent need for the fish. Around 52% of the global marine fish stocks are classed as being fully exploited and 24% are overexploited, depleted, or recovering from depletion, the United Nations Food and Agriculture Organization (FAO) reports. If the current situation continues, there will be a major collapse in most species fished for food by 2048.

Over 1,000 species of fish are now endangered, either directly because of overfishing or because of the impact that marine fisheries have upon ecosystems. One of the most important, economically, is the Atlantic cod. Large open ocean fish, like tuna, swordfish, and marlin, are also in trouble, along with large groundfish such as halibut, skate, and flounder. Stocks of all these are down to around 10% according to the FAO.

Meanwhile, fish can even pose a health hazard. Fish species exposed to contaminated waters may concentrate toxins in their flesh, including pesticides, mercury, and polychlorinated biphenyls. These substances may enter the water at low concentrations, but as they are absorbed through the marine food chain, they accumulate to levels that may be harmful. Farmed fish may also be contaminated with the antibiotics used to ensure high yields.

Marine fisheries can give rise to other problems. Sometimes they harm or destroy coastal habitats, mangrove swamps, and coral reefs, the latter being especially endangered by bottom trawling. The method by which fish are harvested is also not always sustainable. For instance, nets used to catch shrimp, tuna, and scallops may harm other species. Unusual fish species from coral reefs may be taken to stock aquaria. Meanwhile, fish farms may deplete wild fish stocks when they take supplies for ponds. There are, however, a few fish species left that can be taken sustainably from the marine environ-

ment. These include farmed catfish or tilapia, Pacific pollack, squid, crayfish, crabs, and wild salmon.

The way forward for marine fisheries is to become more sustainable and consumers more aware. The Environmental Defense Fund recommends avoiding top predator species including swordfish, marlin, shark, bluefin, and albacore tuna when choosing a seafood meal. These species grow slowly and take several years to reproduce. Groundfish and deepwater fish that have been affected by overfishing include orange roughy; grouper; flounder or sole; cod; haddock; pollack, which is used in various fish products; and monkfish.

Many countries where marine fishing is an important industry now have legislation in place to protect stocks. In the United States, this is the Magnuson-Stevens Fishery Conservation and Management Reauthorization Act of 2006, which sets catch limits and requires sustainable management to protect against over-fishing.

See Also Commercial Fisheries; Inland Fisheries; Marine Ecosystems; Overfishing



Cunningham, W.P., and A. Cunningham. Environmental Science: A Global Concern. New York: McGraw-Hill International Edition, 2008.

Kaufmann, R., and C. Cleveland. Environmental Science. New York: McGraw-Hill International Edition, 2008.

Rice, Tony. Deep Ocean. London: Natural History Museum, 2000.

Web Sites

Environmental Defense Fund. “Eco-Friendly Seafood Selector.” 2008. (accessed March 31, 2008).

WWF. “Our Oceans Are Being Plundered.” February 29, 2008. (accessed March 31, 2008).

Susan Aldridge