Harvesting Wild Marine Species

Worldwide trade in wildlife, worth over $10 billion annually, is responsible for the decline of many species, including many marine animals. The pattern in many cases is distressingly similar. After a resource is identified, a commercial market for it is developed. With consumption, the supply diminishes and the price rises, creating a strong incentive to overharvest the resource. A striking example is found in the enormous demand for seahorses in countries where dried seahorses are used in traditional medicine. Use of seahorses for medicinal purposes results in roughly 16 million seahorses being consumed per year. Seahorse populations throughout the world are so at risk that international trade in seahorses is now monitored and regulated by international agreements.

Governments and industries often claim that they can avoid overharvesting of wild species by not harvesting more than the maximum sustainable yield, the greatest amount of a resource that scientists believe can be harvested each year and replaced through population growth without detriment to the population. In highly controlled situations, such as plantations of timber trees, it may be possible to approach maximum sustainable yield. However, in many real-world situations, harvesting a species at the theoretical maximum sustainable yield is not possible, because of unpredictable factors such as weather conditions and illegal harvesting. Also, commercial entities and government officials often lack the key biological information that is needed to make accurate calculations. Not surprisingly, attempts to harvest at high levels can lead to abrupt species declines. Many other nontarget species may be severely damaged or killed during fishing when they become bycatch-organisms caught by accident and then discarded-or when their habitats on the seafloor are scoured by fishing nets dragged along the sea bottom. Sometimes, changes in fishing practices can result in dramatic reductions in bycatch. For example, large numbers of sea turtles were dying when they were being accidentally caught by Hawaii-based swordfish boats. When the boats changed from using J-shaped hooks with squid bait to using circular hooks with fish bait, turtle captures declined by over 80 percent.

Stocks of marine fish are notable for their decline following periods of intense exploitation, often despite government and scientific supervision. The Canadian fishing fleet continued to harvest large amounts of cod off Newfoundland (a Canadian island) during the 1980s, even as populations declined. Eventually, cod stocks dropped to 1 percent of their original numbers, and in 1992 the government was forced to close the fishery, eliminating 35,000 jobs. In order to satisfy local business interests and protect jobs, governments often set harvesting levels too high, resulting in damage to the resource base. It is particularly difficult to coordinate international agreements and to monitor compliance with yield limits when species migrate across national boundaries and through international waters. One of the most effective strategies may be to monitor populations of animals and plants on a regular basis and then alter harvest levels in response to the abundance of targeted species.

One of the most heated debates over the harvesting of wild species has involved the hunting of whales. The debate is due in part to the strong emotional attachment to whales that many people in western countries have. After recognizing that many whale species had been hunted to dangerously low levels, the International Whaling Commission finally banned all commercial whaling in 1986. Despite that ban, certain species remain at densities far below their original numbers. Those species include the blue whale and the northern right whale, which have been protected since 1967 and 1935, respectively. The densities of other species, such as the gray whale, appear to have recovered, however. The slow recovery of some species may be due to continued illegal hunting. Factors other than hunting may also be responsible for unnatural whale mortality. For example, right whales frequently are killed when they collide with ships, and each year thousands of dolphins and an unknown number of whales suffocate when they become entangled in deep-sea fishing equipment intended for tuna, cod, and other commercial fish. Efforts to require "dolphin friendly" fishing methods have been only partially effective and have caused tension in trade relationships between countries. As many overexploited species become increasingly rare, perhaps it will no longer be commercially viable to harvest them, and their population will recover.