In addition to overfishing, other factors play a part in the diminishing stocks of commercial fish species. Some are beyond human control. Most are traceable to human activity. For example, developing human populations along the world's coasts have added to the pollution of inland rivers and streams; estuaries and lagoons that previously sheltered and fed juvenile fish have been filled in and developed. Almost three-quarters of the species in the US fisheries must live in estuaries at some stage in their growth.
By-catch, the netting and killing of unwanted fish, is another factor in the shrinkage of fish stocks. The dolphin and porpoise kill in tuna fishing became well known to canned-tunafish buyers in the 1980s, and the methods in which purse seine nets are used in the tuna fisheries were changed as a result. However, in the US shrimp fishery alone, an estimated 172,000 US tons of juvenile fish are thrown out each year, contributing to a noticeable decreases in the populations of snappers and groupers in the Gulf of Mexico. The estimated by-catch in Alaskan fisheries amounts to over one-half million US tons a year. Worldwide, as much as 30 percent of the fish caught may be wasted as by-catch.
FISHERIES MANAGEMENT
As early as the 1890s it was acknowledged that fishery resources are limited and that they must be managed through international agreements. In 1902 the International Council for Exploration of the Sea (ICES) was formed by the major European fishing countries. The founding of ICES led to many conventions for the regulation of fisheries by quotas and by mesh size of nets, in order to obtain "maximum sustainable yields" - the highest yields consistent with the maintenance of fish stocks. Until recent years, such conventions were effective in the Northeast Atlantic, although they did not operate as well in other regions. The extension of national jurisdictions over fisheries resources to a 200-naut-mi (370-km/230-mi) zone, beginning in the 1970s, further limited the effectiveness of many international conventions.
In the United States the Magnuson Fisheries Conservation and Management Act of 1976 placed all marine resources from three to 200 naut mi offshore under US jurisdiction. Management is effected through eight regional fisheries councils whose members come mainly from the industry. Each council has the power to set quotas for the commercial fish species living within its jurisdiction in order "to achieve optimum yield from each fishery on a continuing basis," and to prepare recovery plans when they have decided that overfishing is depleting stocks. In addition, the councils have granted permits to foreign countries to harvest specified quantities of certain fish species in return for a fee. Countries that have fished under US license included Japan, South Korea, the former USSR, and Poland. In their desire to maintain the prosperity of the fleets within their regions, however, the councils have not been harsh in their recognition of depleted stocks, the quotas they set, or their preparations for stock recoveries. In 1994, however, the New England Fisheries Management Council began a process that will lead to closing commercial fishing in the Georges Bank for a number of years.
Fishing in international waters has also proved difficult to control. While it is believed, for example, that most nations have obeyed the UN moratorium on drift-net fishing, monitoring compliance remains an unsolved problem. The US Navy's Sound Surveillance System, a 48,000-km network of undersea cable, is capable of tracking drift-net operations, but budget considerations may eventually force the sound surveillance system shutdown.