The Threats Facing Whales
A World Wide Fund for Nature Species Status Report
Until recently whaling has been by far the greatest danger for whales. Even following full protection from whaling, when whale populations have been reduced to very low levels, they do not begin to recover for a number of decades, if ever.
In some cases, recovery may be slowed by the continuing annual kills allowed by the IWC for "aboriginal subsistence need", which in 1995 include around 65 bowheads off Alaska, 165 minkes from the depleted population off West Greenland, 19 fins off Greenland, and 2 humpbacks off St Vincent. Norway's commercial hunt for 301 minkes from the depleted Northeastern Atlantic population is also slowing recovery there.
Other threats to Cetaceans
Even when the prohibitions on whaling are fully enforced, or hunting of smaller cetaceans is controlled, whales and dolphins are vulnerable to the more recent threats to marine species now resulting from increasing human activities described below. Many cetacean species migrate annually between pelagic and coastal areas, and so are subject to different threats at different times of the year. There can be very few populations left of any cetacean anywhere in the world that are not affected by at least one of these threats, and most are facing a range of hazards.
Bycatches in Fisheries
During the past 25 years, the fishery bycatch problem has become one of the most serious threats worldwide to cetaceans, as well as to non-target fish, turtles, and seabirds. This period coincided with the rapid expansion of many fisheries, and in particular with the development of synthetic driftnets and gillnets.
Large-scale high seas driftnets have caused the deaths of hundreds of thousands, if not millions, of cetaceans of many species. In 1990, for example, the IWC estimated the mortality of cetaceans in driftnets (mostly of Japanese and Taiwanese origin) in the Pacific and Indian Oceans and the Mediterranean to be between 315,600 and 1,060,200. There was no estimate for the Atlantic. At the start of 1993, the UN established a global moratorium on large-scale driftnets outside 200-mile Exclusive Economic Zones (EEZs), but implementation of this ban needs to be closely monitored. Driftnetting continues with large cetacean bycatches, for example in the Italian swordfish fishery in the Mediterranean, in the French tuna fishery in the northeastern Atlantic, and within the EEZs of Russia and Japan.
River and coastal wildlife often suffers from habitat degradation in the same way as terrestrial species. Amongst cetaceans, the river dolphins are especially vulnerable, and have been seriously depleted because of vessel traffic, riverbank development, damming, and irrigation projects. The Yangtze and Indus river dolphins are both in danger of extinction. In addition, coastal development such as the widespread draining of mangrove swamps has reduced the food supply of young fish for cetaceans. Major engineering work, of which the construction of the new Hong Kong airport is a prime example, can seriously threaten resident coastal dolphins.
There has been a series of mass die-offs of marine mammals since the 1980s, including bottlenose dolphins along the Atlantic coast of the US in 1987 and 1988, striped dolphins in the Mediterranean in the early 1990s, harbour porpoises in the Black Sea, humpback whales in the western North Atlantic, and dolphins on the Texas coast in 1994. Most of these have been linked to high levels of PCBs found in the dead animals. The endangered beluga whales of the St Lawrence estuary are now among the most contaminated animals on earth, with tumours, reproductive problems, and heavy metal poisoning.
The effects of industrial chemicals and pesticide run-off on whales and dolphins are subtle and insidious, but are potentially amongst the gravest threats to their survival. The evidence is growing that even low levels of contaminants, especially PCBs, DDT, and other persistent organochlorine chemicals, are increasing susceptibility to disease and decreasing fertility by interfering with the hormonal systems of many animals. If this continues, it is possible that some apparently stable populations of long-lived animals including whales could suddenly crash with very little warning.
Chemicals such as the organochlorines become more and more concentrated in the bodies of animals the higher they are in the food chain. Until recently it was thought that the baleen whales were not so much at risk from pollutants as the toothed cetaceans such as belugas, sperm whales, and dolphins, since baleen whales feed on krill, plankton, and small fish at the top of a much shorter food chain. However, the most recent research suggests that baleen whales including grays and humpbacks are also affected. The chemicals accumulate in the whales' blubber while they feed heavily during the summer months, and are then released into their milk when they migrate to the winter calving grounds where there is little food.
Many whales and dolphins depend on sound for navigation and communication, and all the toothed species use echolocation ("seeing" by sending out sounds and receiving echoes from the objects around) for finding their food. If the underwater noise levels from boat traffic and industrial activity are too intense they may seriously affect the ability of cetaceans to communicate or to echolocate. Both oil drilling ships and seismic surveys are strongly suspected of having particularly severe effects on cetaceans. For example, in 1992, humpback whales off Newfoundland, Canada, were found with damaged ear structures after underwater blasting was used in constructing oil installations.
Global climate change
As the evidence accumulates of severe perturbations in ocean currents caused by global warming, whales cannot be expected to be immune from the consequences. For example, recent research shows increases in surface water temperature off the Californian coast linked to a significant decline in zooplankton, which is likely to affect all the species (fish and whales) dependent on it. There are also indications that the higher levels of solar radiation caused by the dramatic reduction in stratospheric ozone over the Antarctic has already led to significant declines in phytoplankton production. Phytoplankton is the basis of the entire food chain in the oceans.
Accidents and disturbance
Many of the few remaining northern right whales in the North Atlantic have scars from boat propellers. Collisions with ships are a serious threat to them and other depleted whale populations. Another area in which caution is needed is the fast-growing whale- and dolphin-watching industry. Whale watching can provide valuable economic, scientific, and educational benefits, but care is needed to make sure that the additional boat traffic is regulated and the whales protected from harassment. In practice, whale-watching is mostly well managed, but in a few places much tighter regulation is needed, such as the dolphin- and pilot whale-watching in the Canary Islands.
Whales in Danger Information Service