There is, however, one fishery which sets its nets around dolphins intentionally because it is the quickest and cheapest way to catch the most profitable fish. In the Eastern Tropical Pacific (ETP), an 18 million square kilometre (8 million square miles) area of water stretching from Mexico to Chile, between 80,000 and 130,000 dolphins are killed by the yellowfin tuna industry every year.
For reasons that are unexplained, schools of large yellowfin tuna which migrate through the ETP often swim just below herds of dolphins, a phenomenon believed to occur only in this part of the world. Fishermen, who have known of this association since the 1920s, used to take advantage of it without harming the dolphins.
The surface disturbances created by the dolphins were used to locate the schools of tuna. Operating from small coastal vessels, the fishermen would throw live bait overboard, sending the tuna into a feeding frenzy during which they would bite at anything, including the hooks lowered to catch them. The dolphins were able to detect the hooks with their sonar and were 'rewarded', as they too fed on the live bait.
The fishermen realized that the tuna swimming underneath the dolphins were almost exclusively yellowfin and were of a greater size than those yellowfin which swam alone. Thus they concentrated their efforts on looking for the tuna associated with dolphins because of the higher profits to be gained from landing the larger fish.
Then, in the late 1950s, the nature of the fishery changed from small-scale to highly commercial, with the development of the 'power block', a hydraulic pulley which permits the smooth and rapid retrieval of a large nylon purse-seine net, over a kilometre (3,300ft) in length. As a result, a mutually advantageous relationship was replaced by one that was to prove fatal for the dolphins.
Rather than hauling tuna aboard individually, it became possible to deploy a net around an entire herd of dolphins and draw, or 'purse', it closed at the bottom, thereby trapping both tuna and dolphins.
Purse-seining allowed far more tuna to be caught than was possible through bait-fishing, was less labour-intensive and thus more profitable. With the realization that bountiful and financially rewarding catches awaited those willing and able to take advantage of the tuna-dolphin bond, the fishery changed dramatically. The results were record catches of yellowfin and record numbers of dead dolphins.
Since 1959, it is estimated that over six million dolphins has died in the nets of the tuna fishery. Indeed, so efficient did it become that, by 1961, the Inter-American Tropical Tuna Commission (IATTC) - the regulatory body responsible for the management of tuna fisheries in the ETP - expressed concern about the status of yellowfin stocks.
The method used to capture the tuna has changed little during the part 30 years. Once a herd of dolphins is spotted from the purse- seiner or from a helicopter, speedboats are launched from the vessel. They give chase and drive in constant circles around the herd. Underwater explosives, thrown from the helicopter or speedboats, may also be used to herd and disorient the dolphins. After a chase that may sometimes last for hours, the exhausted dolphins slow down and form a protective circle. The purse-seine net is then easily deployed around the entire herd and sealed at the bottom.
Many dolphins become entangled in the net and suffocate. Others may be crushed by the weight of the tuna in the crowded net, or by the power winch, as the net is hauled in. Flippers and beaks may be torn off as the dolphins struggle to free themselves. Those that escape one such encounter may soon find themselves netted again.
The huge mortality of dolphins caused by this fishery went largely unnoticed until brought to the public's attention by William Perrin, a young US fisheries scientist, who signed on with the US tuna fleet in 1966 and 1967 to study the behaviour of dolphins as the basis for his doctoral dissertation. In 1969, Perrin revealed that in the course of netting a single school of tuna, the fishermen would sometimes kill as many as 1,000 dolphins. In all, he estimated that roughly 250,000 dolphins were dying in the nets of the US tuna fleet every year.
The ensuing public outrage over the number of dolphins killed was a major impetus for the development and passage of the US Marine Mammal Protection Act (MMPA) of 1972. Considered a landmark piece of legislation, it offered, on paper at least, strict protection for all marine mammals in US waters and placed a moratorium on the killing, capture and even harassment.
One of the MMPA's 'immediate goals' was to reduce to 'insignificant levels approaching zero' the number of dolphins killed by the yellowfin tuna fishery. The act further prohibited the accidental or intentional taking of any 'depleted' stock of dolphins.
In reality the implementation of these measures has proved to be extremely difficult. Initially the tuna industry was given a two year exemption period, in order to allow the fishery time to develop techniques that would reduce dolphin mortality and thus solve the problem. During this time an estimated half a million more dolphins perished. A lawsuit initiated by conservationists forced the introduction of a system of rapidly decreasing annul quotas and an observer programme to ensure more accurate estimates of mortality and compliance with the law. At that time, more than 90 per cent of the fleet consisted of US vessels and thus these measures were expected drastically to reduce the total number of dolphins killed.
The first quota, in 1976, allowed the killing of 78,000 dolphins. This was steadily reduced over the next five years until it stood at 20,500 in 1981, which is where it remains today. Unfortunately, reductions in the US quota have not led to significant reductions in the total number of dolphins killed annually.
For one thing, while the US quota has remained steady, the size of the US fleet in the ETP has declined dramatically from 110 vessels in the early 1970s, each of which could hold from 600-1,000 tonnes of tuna, to 27 in 1990; as a result, each US seiner may and does kill more dolphins than before.
Even more importantly, the reduction of the US fleet has led to substantial changes in the composition of the international tuna fishing fleet. The US now accounts for less than a quarter of the 110 or so purse-seiners operating in the ETP. Many US vessels have simply re-registered under the flags of other nations, either to benefit from cheaper labour and fuel costs, or as some have suggested, to avoid US laws such as the MMPA. Between 1972 and 1980, 27 US vessels transferred to foreign registry, 10 vessels changed flags in 1984 alone.
The largest tuna-seining fleet in the ETP now carries the Mexican flag. The US fleet in now the second largest, followed by Venezuela, Ecuador, the South Pacific island state of Vanuatu, Panama, the Republic of Korea and Spain.
Several of these countries have now constructed giant 'super seiners', each of which can hold almost 2,000 tonnes of yellowfin. The total capacity of the international fleet in the ETP is now more than 150,000 tonnes from a single voyage; the 1988 yellowfin catch in the region was a record 295,000 tonnes. According to the official figures of the IATTC, between 80,000 and 120,000 dolphins are killed every year by the international purse-seine fleet in the ETP. However, it is widely suspected that these figures underestimate the true number of dolphins killed, for the following reasons.
Not all vessels carry official observers, and estimates of the total number of dolphins are extrapolated from the figures that these observers provide. Such a calculation is based on the assumption that unobserved vessels 'perform; in the same manner as observed vessels. However, when international observer coverage was expanded to include the boats of non-US fleets, and in particular Mexican boats, under a programme developed by the IATTC, the total recorded mortality estimates leapt from 57,000 in 1985 to 130,000 in 1986.
Furthermore official estimates do not account for, or record, mortally wounded animals. Dolphins who have lost their beak, flippers or tail, or whose nursing mothers have been killed, are not counted in the mortality figures if they are alive when released.
The industry has attempted to limit the number of dolphins killed in the ETP. The early 1960s saw the development of the 'backdown' procedure, in which the purse-seiner reverses direction when the net has been sealed at the bottom. This causes the open top of the net to elongate into a narrow channel. The flow of water causes the far edge of the net to sink, thus allowing the dolphins to escape over it. In 1971, vessels began replacing the upper-most part of the net with finer mesh in which dolphins were less likely to become entangled.
The great majority of 'sets' made by US vessels kill relatively few dolphins. The vast majority of the 20,500 dolphins killed annually by the US fleet result from a few 'disaster sets' in which these procedures fail because of unforeseen or unavoidable factors such as weather conditions or gear breakdowns. In such situations entire dolphin herds may be killed.
US law now requires that any nation wishing to export tuna to the US must demonstrate that it has a regulatory programme and that kill rates are comparable to those of the US fleet. Nevertheless, even if all the other nations could achieve the 99 per cent release rate claimed by the US fleet, the total mortality rate would still remain at a level of 80,000 dolphins a year.
The most commonly caught species in the ETP, and therefore the ones which warrant the most concern, are the spotted, spinner and common dolphins. Of greatest importance to the fishery is the 'northern offshore' spotted dolphin, as 90 per cent of all dolphin 'sets' involve pure or mixed herds of this stock. In 1979, fisheries scientists reported that this stock was 'depleted' or below its optimum sustainable population (OSP); it has since declined further but has not yet been afforded the protection it warrants. To do so would sharply curtail the practice of 'setting' on dolphins.
Even more worrying is the status of the eastern spinner stock, which is estimated to have suffered a decline of 80 per cent since modern tuna-seining began. Although this stock has been formally designated as 'depleted', and thus has total legal protection, an estimated 20,000 are still being killed annually.
Regulation of the tuna-dolphin problem is extremely difficult. The IATTC runs a highly-regarded scientific programme designed to address the issue but its mandate is primary to achieve the Maximum Sustainable Yield of tuna from the Eastern Pacific. Several
participants in recent IATTC meetings have argued that to expend energy on protecting dolphin populations is in direct conflict with that mandate. Furthermore, several important tuna fishing nations are not members of the Commission - including Mexico, the country with the largest fleet in the region.
There are other, more complex, issues involved. The large yellowfin tuna which swim beneath dolphin herds are an exceptionally valuable commodity and command a very high market price. They are easier to handle and process than the equivalent weight of small fish and, as a result, many fish processors are set up to deal only with large yellowfin.
These processors have encouraged the development of large-scale purse-seine operations in Latin America, furnishing loans for the purchase of vessels with a great enough capacity to exploit the deeper offshore waters where the largest tuna are to be found.
In order to repay these loans, the fishermen must make the maximum possible profit in the shortest possible time and they are therefore forced to catch large yellowfin, as opposed to smaller tuna.
That fishing for smaller tuna is not economically viable was demonstrated in 1986. The US had exceeded its dolphin kill quota by October that year and was thus prohibited from making further dolphin sets. Despite the ban, the fleet caught more tuna in the final quarter of that year than in the equivalent periods of the two years before or after. Despite the increased tonnage, the industry claimed to have lost revenue since the catch was composed of skipjack and smaller yellowfin tuna, which has a lower market value.
As long as this situation continues the only solution to the tuna- dolphin problem is to devise new fishing methods which will enable large yellowfin to be caught in a way which does not harm, or possibly even involve dolphins. It is now know, for example, that tuna will congregate under virtually any floating object. Fish Aggregating Devices (FADs), large rafts beneath which fish gather, are already being used on a trial basis in some parts of the world.
However, because the yellowfin tuna fishery is so highly competitive, no single vessel or fleet is likely to experiment with new methods unless its competitors do so. In the absence of any international regulatory body with enough authority to impose such innovations, many conservationists argue that the price differential between different sizes of tuna must be reduced or even reversed.
One important step towards this has been the introduction of a Bill in the US Congress proposing that all tuna produce sold in the US be labelled to state whether or not it was caught by methods that might have killed dolphins. It is hoped that this will encourage consumers to avoid buying certain tuna products and thus make it more profitable to catch tuna by other methods. Such a shift in the market may additionally provide the necessary economic incentives for the development of alternative fishing technologies.
ADDENDUM: under a 1994 addition to the MMPA, it is now illegal for anyone to sell any tuna in the United States which was caught by setting on dolphins.
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