Aquatic Species and Their Environments - Overfishing—too Many Boats, Not Enough Fish

Worldwide, humans obtain 16 percent of their animal protein from fish. As the human population explodes, the fishing industry has tried to keep up with demand. Up to a certain point, fishermen are able to catch more fish without damaging the ecological balance. This is known as the maximum sustainable yield. Catches beyond the maximum sustainable yield represent overfishing. Overfishing removes fish faster than they can reproduce and causes serious population declines. Furthermore, once fishermen deplete all the large fish of a species, they often begin to target smaller, younger individuals. Targeting young fish undermines future breeding populations and guarantees a smaller biological return in future years. Swordfish have been seriously depleted in this way. In the early 1900s, the average weight of a swordfish when caught was around 300 pounds. By 1960, it was 266 pounds, and at the close of the twentieth century it was 90 pounds.

Technological advances have enabled numerous marine fisheries to be depleted in a short amount of time. In addition, the eight regional councils that regulate commercial fishing, all of which are dominated by the fishing industry, have been either unable or unwilling to set limits for themselves. As a result, most fishing areas are free-for-alls.

The U.S. government attempted to eliminate overfishing in U.S. coastal waters by passing the Magnuson Act in 1976. The Magnuson Act expanded the coastal economic zone claimed by the United States from three miles offshore to 200 miles offshore, preventing foreign fishing fleets from exploiting these waters. However, with foreign fleets gone, American fishermen built up their own fleets, buying large, well-equipped vessels with low-interest loans from the federal government. For several years U.S. fishermen reported record catches. Then these declined. Government officials now report that most of the major commercial fishing areas in the United States are in trouble. According to the National Marine Fisheries Service (NMFS), about 40 percent of the nation's saltwater species have been overfished.

From Drift Nets to Longlines

Drift nets are the world's largest fishing nets, reaching lengths of up to 30 miles. Conservationists refer to them as "walls of death" because they indiscriminately catch and kill marine species. Over 100 species—including whales, sea turtles, dolphins, seabirds, sharks, salmon, and numerous other fish species—have been killed in drift nets. Drift nets were eventually banned because of their destructiveness to wildlife.

After the banning of drift nets, many fishermen turned to longlines. Longlines are fishing lines with a single main line attached to many shorter lines that terminate in baited hooks. They are used to catch wide-ranging oceanic species such as tuna, swordfish, and sharks, as well as bottom dwellers such as cod and halibut. A single boat can trail thousands of hooks from lines stretching 20 to 80 miles.

Longline fishing kills fewer marine mammals than drift nets but captures more surface-feeding sea birds, particularly the rare albatrosses. Longline fishing has in fact resulted in the decline of numerous albatross species, almost all of which are now listed by the World Conservation Union (IUCN) as endangered. Australian scientists estimate that longline fishing kills more than 40,000 albatrosses each year. Longline fishing has also caused rapid declines in some fish species. Longlining is an old practice, but modern technology has vastly increased its efficiency and ecological impact.

Fish Declines and Deep-Sea Harvesting

As catches of shallow water fishes decline, trawlers have increasingly been used to scour the deep seas for new varieties of fish, such as the nine-inch long royal red shrimp, rattails, skates, squid, red crabs, orange roughy, oreos, hoki, blue ling, southern blue whiting, and spiny dogfish. Although limited commercial deep-sea fishing has occurred for decades, new technologies are making it considerably more practical and efficient. As stocks of better-known fish shrink and international quotas tighten, experts say deep ocean waters will increasingly be targeted as a source of seafood.