header: Cetaceans (Whales)
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Mammalian order Cetacea

THREATS

The major threats to cetaceans include direct exploitation, bycatches in fisheries, competition and culls, and habitat loss and degradation. There are four species of cetacean (Baiji, Vaquita, Northern Right Whale and Indus River Dolphin) that are considered by the Cetacean Specialist Group to be seriously endangered.

Direct exploitation: Until recently, this was the greatest threat to the survival of the large cetaceans. For example, the Northern Right Whale has been reduced to approximately a few hundred animals in the North Atlantic and probably to an even lower level in the North Pacific, and to date has shown no signs of recovery despite many years of protection. Presently, there are extensive takes of "small" cetaceans in Japanese waters, mainly for meat. One such example of this is the take of Dall's Porpoise in Japanese waters resulting in over 17,000 animals killed each year. Similarly, it is thought that the Beluga Whale and the Narwhal are threatened by whaling.

Bycatches in Fisheries: 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. Estimates of total kill and kill rates can only be approximate. Technical approaches, such as employment of warning devices in netting and modification in floats, weights and characteristics of the netting are unlikely to eliminate the bycatch problem, however the closure of certain critical areas to coastal gillnetting (e.g. the ban on large-mesh Totoaba nets in the upper Gulf of California, Mexico, habitat of the Vaquita) has helped. Concern about the expansion of large scale driftnet fishing during the 1980s led the United Nations General Assembly to establish an indefinite global moratorium on the use of large-scale driftnets outside the exclusive economic zone (EEZ) or the 200 mile limit of any country after 1992. Discarded drift nets ("ghost nets") are also capable of entangling cetaceans and can remain "active" for several years. Numerous individuals and groups on the east coast of Canada and the United States have mounted effective rescue operations directed mainly at large whales that become entangled in cod traps and ground fish gillnets.

Habitat Loss and Degradation: Coastal, riverine and estuarine cetacean species are particularly affected by this factor. Coastal developments can destroy fish nurseries leading to a reduction in food supply; damming of rivers can result in the isolation and fragmentation of populations, and the prevention of seasonal migrations. For example, the Indus River Dolphin is now extinct in parts of its former range through illegal hunting, and fragmentation of the species range from the construction of a barrage. Pollution is also believed to be a potential threat to the survival of many marine and freshwater organisms. From the introduction of pollutants into waterways, substances can enter the food chain and become concentrated in aquatic organisms, such as the cetaceans. The evidence for a link between chemical pollutants and the health of cetaceans is growing, and there is concern that large contaminant loads can increase susceptibility to disease and affect reproductive performance. Polychlorinated biphenyls (PCB's) are of particular concern.

Competition and Culls: The belief that cetaceans compete for resources has prompted the initiation of culling operations in some instances, such as Killer Whales in Iceland and Greenland and various toothed whales in Japan. Some scientists and resource managers advocate that routine culling of cetaceans (and other marine mammals, notably seals) is integral to "ecosystem management". This argument, although considered invalid due to the complexity of the marine ecosystem, has been used mainly in the context of Norway's resumption of commercial whaling for Minke Whales and continuation of the North Atlantic seal harvest.


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