Tuna Fishing Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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Tuna fishing as a major industry did not exist before the 20th century, although there were some catches of “giant” mackerel off areas such as the British Isles that may have been bluefin tuna. Industrial tuna fishing began in the United States in 1903, when tuna was seen as a possible replacement for dwindling sardine catches, but the industry really took off during World War II, when canned tuna became an important source of protein. Tuna have been caught with driftnets, purse seine nets, long lines, and traps. The United States and Japan are currently the two largest consumers of tuna, accounting for 31 percent and 36 percent of the world catch, respectively. In 2000, an estimated 3.6 million tons of tuna were caught, 66 percent from the Pacific Ocean, 20.7 percent from the Indian Ocean, 12.5 percent from the Atlantic, and 0.8 percent from the Mediterranean and Black Seas.

Tuna belong to the teleost family Scombridae. Major target species include bluefin, albacore, skipjack, bigeye, and yellowfin. The largest of these are bluefin tuna (Thunnus thynnus), which typically grow to 20 feet (6 meters) and 1,102 pounds (500 kilograms), but some specimens have weighed over 1,499 pounds (680 kilograms). Bluefin in the south Pacific are estimated to be at 15-20 percent of their historic stock size due to overfishing. Moreover, recent research suggests that bluefin quotas in the Atlantic have been set too high, and due to the wide-ranging migration patterns of these fish, individuals from depleted populations may move to areas of high fishing pressure. Bluefin tuna are primarily traded with Japan and sold for consumption as sushi and sashimi.

Albacore tuna (Thunnus alalunga) are subtropical and have distinctive long pectoral fins but are much smaller than bluefin, at two feet (0.7 meter) in length and 22-44 pounds (10-20 kilograms), although they can grow up to five feet (1.4 meters) long and weigh 132 pounds (60 kilograms). This species was depleted by driftnet fisheries but may now be recovering with the introduction of largescale driftnet bans. This species is frequently targeted for the canned tuna industry.

The main target species for canned tuna are the smaller skipjack (Katsuwonus pelamis), which are typically one foot (35 centimeters) long and about seven pounds (three kilograms) but can grow up to 40 pounds (18 kilograms), and the bigeye (Thunnus obesus). Bigeye tuna typically grow to about three feet (0.9 meter) and 33-44 pounds (15-20 kilograms) but have been caught at weights of up to 734 pounds (333 kilograms). This species dwells in deep, cool water and has a thick fat layer for insulation, making it a favorite of the sashimi market.

Yellowfin tuna (Thunnus albacares) are found in tropical and subtropical waters, growing up to eight feet (2.4 meters) and 441 pounds (200 kilograms). Yellowfin in the eastern tropical Pacific (ETP) are typically found swimming underneath schools of spinner (Stenella longirostris) and spotted dolphins (S. attenuata).

Dangers to Dolphins

It is not certain why yellowfin tuna swim under schools of dolphins, but it may be that the dolphins provide the tuna some protection from predators (the dolphins appear to gain no benefits from the tuna). This association is so strong that purse seine fishing operations targeting yellowfin set their nets around dolphin schools to catch the associated tuna, but also catch and kill many dolphins. Indeed, this method of tuna fishing has killed more dolphins than any other human activity.

It is estimated that six million spinner and pantropical spotted dolphins alone were killed as bycatch before conservation measures were introduced, with up to half a million dolphins killed a year in the 1960s and 1970s. This high level of dolphin mortality was one of the key factors behind the introduction of the U.S. Marine Mammal Protection Act in 1972 (MMPA). The MMPA helped to reduce the amount of dolphin by-catch, and due to strict limits on mortality, fewer and fewer U.S. fishing vessels participated in the ETP fishery, although vessels from other nations remained in the region.

In 1990 the concept of “dolphin safe” tuna was introduced, which had a major effect on purchases of tuna worldwide, through consumer choice. Dolphin safe tuna was initially defined as tuna caught by methods other than setting purse seine nets on dolphins-it was an effort to eliminate a fishing method considered inherently harmful to dolphins. After use of the “dolphin safe” label became widespread, first voluntarily by tuna companies and later by law in the United States, fishers in the ETP made efforts to reduce dolphin mortalities, achieving a 95 percent decrease, but nonetheless did not cease setting purse seine nets on dolphins.

Furthermore, to reduce dolphin mortality, the Inter-American Tropical Tuna Commission (IATTC), the body governing tuna fishing in the ETP, adopted the International Dolphin Conservation Program (IDCP) in 1992, a voluntary by-catch reduction scheme codified in the so-called La Jolla Agreement. Nations fishing in the ETP agreed to voluntary limits on the number of dolphin deaths (the dolphin mortality limit, or DML) that could be inflicted by each vessel in the ETP tuna fishery. The aim was to reduce these limits each year until a zero mortality level was reached. Measures to monitor and reduce dolphin mortality included an onboard observer program to record dolphin kills, and the “backing down” of purse seine vessels, that is, sinking the top of the net to allow encircled dolphins to swim over the top and escape. In 1995, the Panama Declaration made these measures mandatory.

The Panama Declaration also introduced a new definition of “dolphin safe” that used an “observed mortality” standard rather than a “fishing method” standard. If observers did not see any dead dolphins in a net set, then the tuna from that set would be considered “dolphin safe.” The U.S. Dolphin Conservation Act of 1997 stated that the United States would adopt this new definition, if the government made a final finding that the chase and encirclement of dolphins were not having a significant adverse impact on depleted stocks. In 1999, and again in 2002, the government tried to make such a finding, but both times the finding was challenged in court. In both cases, the courts ruled against the government, which means the original definition of “dolphin safe” has so far been retained.

The court challenges were based on the fact that, although dolphin mortality levels have been greatly reduced in this fishery, the dolphin populations have not recovered as expected. Scientific evidence strongly suggests that chasing and herding dolphins prior to setting nets separates mothers from calves and leads to debilitating stress, even when dolphins are released alive during the “back-down.” Also there was evidence of underreporting of dolphin mortalities. The scientific data and underreporting evidence were virtually ignored when the U.S. government made its findings, a decision heavily criticized by the courts.

Mercury Contamination

Another controversial environmental issue related to tuna fisheries is a high level of mercury contamination in some species. A quarter of canned albacore tuna examined in a recent study exceeded U.S. health regulation limits. Other species found to be highly contaminated include blackfin tuna (Thunnus atlanticus) and little tunny (Euthynnus alletterus) off the coast of Florida, of which 81 percent and 75 percent, respectively, contained more mercury than U.S. health regulation limits. As a result of possible health risks from mercury contamination in large predatory fish such as tuna, in March 2004 the U.S. Food and Drug Administration (FDA) issued guidelines recommending pregnant women, nursing mothers, and children limit their weekly intake of some tuna products. Other countries, such as those of the United Kingdom, have issued similar warnings.

Bibliography:

H. Adams, “Total Mercury Levels in Tunas from Offshore Waters of the Florida Atlantic Coast,” Marine Pollution Bulletin (v.49, 2004);
F. Archer et , “Annual Estimates of the Unobserved Incidental Kill of Pantropical Spotted Dolphin (Stenella attenuata) Calves in the Purse-Seine Fishery of the Eastern Tropical Pacific,” Fishery Bulletin (v.102, 2004);
A. Block et al., “Electronic Tagging and Population Structure of Atlantic Bluefin Tuna,” Nature (v.434, 2005);
Burger and M. Gochfeld, “Mercury in Canned Tuna: White versus Light and Temporal Variation,” Environmental Research (v.96, 2004);
V. Gewin, “Pacific Dolphins Make Waves for S. Policy on Mexican Tuna,” Nature (v.427, 2004);
A. Myers and B. Worm, “Rapid Worldwide Depletion of Predatory Fish Communities,” Nature (v.424, 2003);
John R. Twiss, Jr. and Randall R. Reeves, Conservation and Management of Marine Mammals (Smithsonian Institution Press, 1999);