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Dolphins, Porpoises, and Whales - IUCN

Dolphins, Porpoises, and Whales - IUCN

Figure 3B Bycatches in

Figure 3B Bycatches in Fisheries Although some incidental mortality of cetaceans has occurred in fishing activities for a very long time, the significant contributions of such mortality to the depletion of cetacean populations have only been recognized during the past 25 years. We are not aware of any instance before the mid to late 1960s in which the magnitude of bycatches was considered great enough to threaten populations. Alarm over the killing of dolphins in the eastern tropical Pacific tuna fishery (perhaps as many as seven million since the late 1950s; IWC 1992a) stirred interest in other forms of "incidental" mortality. The tuna-dolphin problem is in fact best viewed as a case of deliberate utilization, since the dolphin herds are chased and captured in the purse seines in order to capture the schools of tuna associated with them (see National Research Council 1992). The first large-scale bycatch to have become well known to cetologists, other than the kill of oceanic dolphins in the tuna fishery, was that of Dall's porpoises in the Japanese drift gillnet fishery for salmon in the North Pacific (Fig. 4). Since that discovery, which was actually made in the 1960s by Japanese investigators (Mizue and Yoshida 1965) but not widely publicized until the mid 1970s (Ohsumi 1975), many additional cases have been identified, such as the Italian swordfish driftnet fishery in the Mediterranean Sea (Notarbartolo di Sciara 1990) and the French tuna driftnet fishery in the northeastern Atlantic (Goujon et al. 1993). Also, during the 1980s the scope of the North Pacific drift gillnet problem widened, with more nations becoming involved, additional target species being taken such as squid, billfish, and tuna, and bycatches coming to include other cetacean species such as northern right whale dolphins and Pacific white-sided dolphins (IWC 1992a). Trawlers working in the Bay of Biscay are suspected of making large bycatches of small cetaceans (A. Collet, pers. comm.). In most cases, the cetaceans that die are regarded as nuisances by the fishermen. Time and effort are required to extricate the cetacean carcasses, and fishing gear and catches are sometimes damaged. Since the carcasses of incidentally caught animals are usually discarded at sea, they provide no economic return and are essentially "wasted." In some areas such as Peru, Sri Lanka, and the Philippines, where artisanal gillnet fisheries have made large bycatches of dolphins, the salvage and use of carcasses has led to directed fisheries for cetaceans.

Figure 3C Particularly with the proliferation of synthetic gillnets throughout the world, the bycatch problem has emerged as one of the most serious threats to cetaceans, as well as to seabirds, turtles, fish, and other non-target organisms. It is in many respects less tractable and more insidious than the problem of direct harvests. Useful estimates of total kills and kill rates have proven difficult to obtain. Technical approaches, such as deployment of warning devices in netting and modifications in floats, weights, and characteristics of the netting, are unlikely to eliminate the bycatch problem; seasonal or year-round closure of gillnet fisheries is in many cases the only effective solution (Dawson 1991a; also see Au and Jones 1991). The development and implementation of fishery regulations have, in general, been politically controversial and slow. The closing of certain critical areas to coastal gillnetting operations (e.g. the sanctuary near Banks Peninsula, New Zealand; the ban on large-mesh totoaba nets in the upper Gulf of California, Mexico) has helped. Nonetheless, in most cases in which significant fishing-related mortality of cetaceans occurs within the fisheries jurisdictions of coastal states, effort to date has been devoted primarily to documenting the size and character of the bycatch rather than to reducing or eliminating it. Concern about the expansion of large-scale driftnet fishing during the 1980s led the United Nations General Assembly to pass Resolution 46/215, establishing an indefinite global moratorium on the use of large-scale driftnets outside the 200-mile limit or exclusive economic zone (EEZ) of any country after December 31, 1992. Although no major violations were reported to the United Nations in 1993, implementation of this ban needs to be closely monitored. Numerous reports of unauthorized high-seas driftnet fishing in the Mediterranean Sea by vessels flying Italian and other flags have continued to be made by the media and by NGOs (cf. Pitt 1994). Also, the moratorium has caused some fleets formerly involved in large-scale driftnetting on the high seas to move their operations into the EEZs of countries such as Japan and Russia. Cetacean bycatches will obviously continue and thus require continued monitoring. Several individuals and groups on the east coast of Canada and the United States have mounted effective "rescue" operations directed mainly at large whales. Jon Lien and associates at Memorial University of Newfoundland were notified of 1,084 entrapments of large cetaceans

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