The mid-1970s saw the dramatic expansion of Latin America's fishing industry, particularly in the eastern Pacific, as several countries sought to integrate their economies into the international market to obtain foreign currency in order to pay off their debts and to find alternative food sources for their populations.
This expansion has inevitably given rise to concerns over the health of the marine ecosystem in this region. Some fish stocks have already been depleted and local populations of several species of small cetaceans have been effected, mainly by the increased use of monofilament gill nets.
Information on the exact numbers of dolphins killed is hard to come by but preliminary research has shown that bottlenose dolphins are caught in shrimp fishing nets in Columbia; several thousand bottlenose dolphins and tucuxi are caught off French Guiana in nets set for sharks, tarpon and mullet; and several hundred franciscana are entangled in shark nets off the coasts of Brazil, Argentina and Uruguay every year.
The effects of entanglement are not restricted to marine species. In the Amazon and Orinoco river systems, a huge increase in the size of commercial fisheries, and the introduction of nylon gill nets, is believed to have had a damaging effect on some populations of boto and tucuxi, although there are no reliable estimates of the numbers involved. Marine mammal scientists Vera de Silva and the late Robin Best, who examined 67 dead dolphins from these river systems between 1979 and 1984, found that all but seven had been killed in nets.
A further development in recent years has been the intentional killing of small cetaceans to provide bait for commercial fisheries.
The killing of dolphins and porpoises for bait has been recorded is Colombia and in venezuela, where 7,000 dolphins of various species are caught every year as bait to catch sharks (although the government has now taken steps to outlaw this practice). The problem has been especially actute in southern Chile where, at one stage, between 4,000 and 5,000 small cetaceans were being killed annually to provide bait for the commercial crab fishery.
Previously, sea lions were caught for this purpose but, when their numbers declined in the late 1970s, the fishery began catching Commerson's dolphins. Over-exploitation of the crabs then led the fishery to a new location and, as a result, Peale's and black dolphins became their main target.
Over the last ten years, new fishing technology, better boats and the introduction of a free-market economy have caused a seven-fold expansion in this fishery.
The flesh of marine mammals is preferred as bait because it can stay in the water for three days before it disintegrates, whereas fish bait deteriorates withing 24 hours. It is also cheaper and more efficient to catch wild dolphins that it is to catch or but fish; for example, one dolphin can provide bait for 350 crab traps.
In recent years, the number of small cetaceans taken for bait has decreased dramatically, probably due to the over-exploitation of local dolphin populations.
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