The commercial methods chiefly used—each with a great variety of modifications—employ encircling nets (purse seine, haul seine, trawl seine), entangling nets (gill and trammel), lines, and traps (for lobster and crab). Trawlers and purse boats take most commercial catches. Since World War II, Japan and Russia (formerly the Soviet Union) have been operating factory ships that freeze or can fish shortly after they are caught. The drying, canning, salting, and preserving of fish comprise a vast industry with, in addition, the manufacture of numerous byproducts, including glue, fertilizer, and in Asia, fish sauces.

Because of the economic importance of the industry, numerous disputes have developed over fishing rights. Increasingly concerns about overfishing, pollution, and declining fish catches have forced governments to pass measures designed to protect and conserve this resource. In the United States, domestic fisheries are generally governed by state regulations, except where the Constitution provides for national control as a result of the treaty-making power and the regulation of navigation, customs, and interstate commerce. State fishery legislation is generally designed to protect the fisheries by regulating the way fish are caught, imposing catch limits, closing some waters to commercial fishing, reducing the times when fishing is legal, and protecting certain species. National governments generally restrict fishing rights within territorial waters to citizens and may establish jurisdiction over portions of the open sea, but the right to take products from the high seas is a subject for international agreements.

Fisheries have occupied an important place in the economic structure of many countries throughout history. The Black Sea fisheries formed an important source of Phoenician and Greek income; Spanish and Sicilian waters yielded fish for Rome; the economy of the Hanseatic League was partly based on the North Sea herring fisheries; cod fishing was a chief industry of New England; and fisheries in the Pacific are vital to Japan. For that reason fishing rights have long been the basis of controversy.

In the modern age such disputes have generally been settled by arbitration or by treaties. Fishing rights that had been enjoyed by the American colonists on the entire Atlantic coast were confirmed in the Treaty of Paris (1783), but the right to dry fish on the Newfoundland coast and on the settled parts of the Labrador and Nova Scotian coasts (except by agreement with the inhabitants) was expressly denied. The outbreak of the War of 1812 led to a new treaty (1818) that further restricted American rights. This convention was replaced by the reciprocity treaty of 1854, which abolished all restrictions except for shellfish. But disputes continued until 1910, when the North Atlantic Coast Fisheries Arbitration at The Hague ended the prolonged controversy. Canada and the United States in 1923 and 1930 signed agreements regulating the halibut fisheries of the N Pacific.

In 1882 Great Britain, Germany, France, Denmark, and Belgium signed the North Sea Fisheries Convention, which ended lawlessness in that area by granting a mutual right of visit, search, and arrest to the public vessels of the treaty powers. A similar treaty, regulating the fishing banks off Iceland and the Faeroe Islands, was signed by Great Britain and Denmark in 1901, and three years later Anglo-French rights in the N Atlantic were set forth in a convention. The fisheries of the Pacific have also been the subject of many international agreements, such as the Japanese right to fish in specified sections of Siberian waters, first granted by the Treaty of Portsmouth in 1905 and continued by later agreements.

To stabilize international rules governing national rights in the oceans, the United Nations convened the Conference on the Law of the Sea in 1974; one of its concerns was to protect fisheries. The oceans have long been used as a dumping ground, but pollution levels in the open seas as well as coastal areas have risen sharply, thus endangering fisheries. Another threat has been overfishing, which in some areas has severely depleted the available catch. In 1996 the U.S. federal government imposed strict limits on fishing in the Gulf of Maine and Georges Bank, in order to protect the declining New England fishing industry; in 1999 restrictions were imposed along the Atlantic and Gulf coasts in an attempt to conserve depleted stocks of shark, tuna, and marlin. Overfishing is not limited to seas off developed nations; the Java Sea in Indonesia, for example, has been fished to the point where local fishermen cannot count on a catch sufficient to feed their families.

For many years, most countries recognized a 12-mi exclusive fisheries zone, but the rise of fleets of factory ships that could catch and process huge quantities of fish severely reduced catches. The Law of the Sea Treaty (1983) established a 200-mi limit inside which countries had the exclusive right to regulate fishing, and in 1997 the United States set a 200-mi territorial zone to protect its fisheries. The United Nations sponsored (1999) a nonbinding agreement among seafaring nations to address the problem of overfishing worldwide by reducing the size of their fishing fleets.

International efforts to protect marine resources have also involved whaling. The International Whaling Commission outlawed most whaling in 1986, but some countries have refused to comply.