ecosystems affect humans. Thus, sustainability of fisheries at an acceptable level of productivity and of the ecosystems they depend on requires a much broader understanding of appropriate and effective management than has been encompassed by traditional, single-species fishery management.
Marine-capture fisheries include commercial, recreational, subsistence, and various small-scale fisheries, with total landings dominated by the commercial sector. In addition to recent reported annual landings of about 84 million t of marine animals (including fish, molluscs, crustaceans, and some other species), marine plants (seaweeds) also are used for food, as well as some marine mammals and turtles. Fishing as a source of food and revenue in less-industrialized countries, traditionally important, has become even more important recently and accounted for 65 percent of the world's catch in 1993.
In addition to fish and invertebrates that were caught and landed, approximately 27 million t of nontarget animals (bycatch) were discarded each year in the early 1990s (discards were probably less in the late 1990s). Furthermore, fishing causes mortality that is never observed because of illegal fishing, animals that die after escaping from fishing gear, or animals that are killed by abandoned fishing gear. Thus, the biomass of fish and invertebrates killed by ocean fishing (not including aquaculture) probably exceeds 110 million t per year.
Various estimates have been made of the total productivity of ocean ecosystems and the maximum long-term potential catch of marine animals. Many of the latter estimates are near 100 million t per year, suggesting that the current annual landings of 84 million t plus unreported mortality are near the maximum sustainable. However, considering species interactions, variations in the ability of individual species to withstand fishing mortality, global overfishing, and ecosystem degradation, it is possible that, under present management and fishery practices, the current catch cannot be exceeded or perhaps even continued on a sustainable basis. Considering individual stocks, about 30 percent globally are overfished,4 depleted, or recovering, and 44 percent are being fished at or near the maximum long-term potential catch rate.
In the United States, commercial marine fishery landings in 1996 were 4.5 million t, worth $3.5 billion (exvessel value, the value of first sales from a vessel). The total economic contribution of recreational and commercial fishing were each approximately $20 billion per year. However, approximately 33 percent of stocks that commercial and recreational fishers depend on were overfished
By overfishing the committee means fishing at an intensity great enough to reduce fish populations below the size at which they could provide the maximum long-term potential (sustainable) yield (see Chapter 2), or at an intensity great enough to prevent their recovery to that size. As described in this report, it follows that overfishing is a function of population size.