Cetaceans (Whales) IUCN Status Category: Variable
Class: Mammalia, Order: Cetacea CITES Appendix: I and II
INTRODUCTION
Cetacea is an order of mammals, comprising over 80 species of whales, dolphins and porpoises. There are three Suborders: the Archaeoceti, the Mysticeti, and the Odontoceti. Cetaceans fall into two categories: mysticetes or baleen whales, and odontocetes, including toothed whales, oceanic and river dolphins, and porpoises. Of these, 13 species are commonly referred to as the great whales and include the bowhead, North Atlantic right, North Pacific right, southern right, blue, fin, sei, humpback, Bryde's, northern minke, southern minke, gray, and sperm whales. The only great whale with teeth is the sperm whale. Although predominantly marine mammals, some small cetaceans live in large river systems of Asia and South America.
The Archaeoceti or "ancient whales" are extinct and known only by fossils. The Odontoceti or "toothed whales" have either no, few or numerous uniform and conical teeth, asymmetrical skull and single nasal passage. The Mysticeti or "baleen or whalebone whales" are named after their feeding apparatus; a series of transverse plates of comb-like baleen (made of similar material to that of the human fingernail) which descend from the roof of the mouth and serve to strain plankton and small fish. Other distinctive characteristics of the baleen whales include a symmetrical skull with no melon (the apparatus used by odontocetes for echolocation) and a pair of nasal cavities. Toothed whales, dolphins and porpoises are a diverse group of over 70 species.
GENERAL BIOLOGY
Cetaceans are mammals that spend all their lives in water, and have evolved many adaptations to this way of life. The body is streamlined, with no hind limbs, reduced forelimbs and a powerful horizontal tail for propulsion. The "nostrils" have become blow holes at the top of the head (except in the Sperm Whale, where it is at the front of the head) to facilitate respiration whilst travelling through water.
The dentition of the toothed whales are also roughly related to feeding habits, with the squid eaters having few or no visible teeth, and those with a more varied diet, particularly those where schooling fish are included, having a generally longer snout and many teeth.
The majority of the large cetacean species are baleen whales, including the Blue Whale (up to 30m), although there are smaller baleen whales, including the 10 meter Minke Whale and the 6 meter Pygmy Right Whale. Many baleen whales travel long distances every year, between summer feeding grounds in polar waters and winter breeding grounds in the tropics. In general, baleen whales seem to live in small social groups, although these can join to form large herds at rich feeding grounds.
The range in size among toothed whales is wide, from the 18 meter (male) Sperm Whale to the smallest dolphins and porpoises at less than 2 meters. They have extremely varied habits; some travel long distances between summer feeding grounds and wintering areas every year, but others are relatively sedentary, perhaps only ranging over tens of kilometres in their lifetimes. Their social life is also highly varied; some species living in small groups or usually alone, and others in schools of several hundred (although these may be composed of a number of smaller social units).
The fossil history of the cetaceans is incomplete and controversial. In general it seems that they evolved from land mammals which may have returned to the water some 70-90 million years ago. The Archaeocetes flourished 45-55 million years ago and the modern forms have been present for 10-12 million years. Cetaceans have exploited all types of productive marine, estuarine, and major riverine habitat. They have adapted to be able to propel themselves through the water at speeds and to depths sufficient to escape predators and catch prey; exchange air without interrupting the smooth forward motion; maintain a fairly constant core body temperature in an environment that readily dissipates heat; and bear young in water.
Vision in air and water varies with species. Some river dolphins which are nearly blind and can distinguish light from dark, while some dolphins appear to have excellent vision. Most species are vocal, producing calls and whistles that may have a social function, such as the "song" of the Humpback Whale, the individual "signature whistles" of Bottlenose dolphins and the "pod identity" call of the Orca. Many toothed whales are known to echo-locate, using pulses of high frequency sound to explore their environment and seek and stun their prey.
DISTRIBUTION
Whales inhabit oceans and seas worldwide, inshore and pelagic. Some species such as minke or humpback whales may be found in all oceans and seas, but most have a more restricted range. Some dolphins are restricted to specific rivers. Most baleen whales are migratory, feeding in colder waters that are rich in plankton, and travelling to lower latitudes to bear their young so that the calves can live in warmer water until they develop a sufficient insulating layer of blubber. Gray whales and humpbacks undertake the longest migrations of all whale species. For example, eastern North Pacific gray whales feed in the Bering Sea between Alaska and Russia and travel all the way to Baja California to have their calves, a distance of 12,000 to 20,000kms.
POPULATION
The methods traditionally used to assess the status of exploited whale populations were based mainly on data from catches. These included: the use of catch per unit effort (CPUE) as an index of abundance; data on pregnancy rates and age of sexual maturity as measures of productivity; age data to estimate recruitment and mortality; and the re-capture of marked animals to estimate population size and define separate stocks. Analyses by the International Whaling Commission (IWC) Scientific Committee over the past few years have shown many of these methods to be unreliable both in principle and in practice. Following the moratorium on commercial whaling in 1986, there has been an increase in efforts to survey whale populations directly. Despite the increased research on some of the directly exploited species, quantitative population estimates are still only available for a minority of species and almost all have wide margins of error. Population estimates of the great whales, where known, are given in Table 1.
Table 1. Current status of the great whales
Species / Status / Approx. Estimated TotalNorthern Atlantic right Eubalaena glacialis / Endangered / Western North Atlantic 300-350. Eastern North Atlantic-near extinction
North Pacific right Eubalena japonica / Endangered / Under 1,000
Southern right Eubalaena australis / Conservation Dependent / About 7,000
Bowhead Balaena mysticus / Conservation Dependent and Critically Endangered in Svalbard, Endangered in Okhotsk and Davis Strait/Baffin Bay / Probably under 8,500
Blue Balaenoptera musculus / Endangered / Probably under 5,000
Fin Balaenoptera physalus / Endangered / Around 50,000 - 90,000
Sei Balaenoptera borealis / Endangered / Roughly 50,000
Bryde's Balaenoptera edeni / Data Deficient / Roughly 40,000 - 80,000
Gray Eschrichtius robustus / Conservation Dependent
Critically Endangered in Western North Pacific / Around 27,000
Humpback whale Megaptera novaeagliae / Vulnerable / Around 28,000
Northern Minke Balaenoptera acutorostrata / Low risk-Near Threatened / 610,000 - 1,284,000
Southern minke Balaenoptera bonarensis / Conservation Dependent / No current estimate
Sperm whale Physeter macrocephalus / Vulnerable / Unknown: maximum 1 -2 million
WCMC and WWF-Int. July 2001
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THREATS
Seven out of the 13 great whale species are endangered. Years of overhunting drove the Atlantic population of gray whales into extinction, and so severely depleted the blue whale in the Antarctic that its original estimated numbers of 250,000 whales have dropped to between 400 and 1,400 animals. Over the past few decades, the great whales and other cetaceans have suffered from new and ever-increasing dangers. Collisions with ships and entanglement in fishing gear threaten the North Atlantic right whale with extinction, while the critically endangered Western North Pacific gray whale is at serious risk probably exacerbated by intensive oil and gas development in its feeding grounds. Scientists estimate this population numbers between 100 to 200 animals. Concern is growing over other hazards including toxic contamination, the effects of climate change and habitat degradation, and marine and river pollution. The Cetacean Specialist Group consider seven species of great whale endangered or vulnerable (see Table 1), and 10 species of small cetacean are endangered or vulnerable, including most of the river dolphins. Three populations of great whales are near extinction: the Svalbard bowhead, Western North Pacific Gray, and the Eastern North Atlantic right.
Bycatches in Fisheries: Entanglement in fishing gear or by-catch kills more cetaceans worldwide each year than any other mortality factor. 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 could help. 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 Degradation and Chemical Pollution: 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 dams. 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, toxic 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 (PCBs) are of particular concern.
Accidents and Disturbance: Ship strikes or accidental collisions have been blamed for nearly 90 per cent of all North Atlantic right whale deaths for which the cause is known (excluding natural factors such as old age).
Direct exploitation: Until recently, this was the greatest threat to the survival of the large cetaceans. The declining status of the great whales was so desperate by the early 1960s that it was among the reasons for the foundation of WWF in late 1961. The highest ever number of whales reported caught was 66,090 in the 19611962 Antarctic whaling season. These were mostly fin and sperm whales, since the blue whales had by then been hunted close to extinction. Despite a number of conservation victories for the whales, including the moratorium on commercial whaling and the declaration of virtually the whole of the Southern Ocean as a whale sanctuary in 1994, whales are still hunted and this remains a potential threat. Since the International Whaling Commission (IWC) moratorium on commercial whaling came into effect in 19851986, by April 2001, 21,573 whales had been caught, mainly by the former USSR, Japan and Norway.
As of 2001, Japan has killed over 5,620 minke whales for socalled scientific purposes, mainly in the Southern Ocean Whale Sanctuary. Norway, which lodged an official objection to the moratorium, has caught 287 whales for "scientific purposes", and hunted over 4,000 Northern minkes for commercial purposes from a depleted population. Norway has continued whale hunting, in spite of the repeated requests by the IWC urging them to stop, and the growing popularity of whale watching in Norway.
Competition and Culls: The belief that cetaceans compete for resources has prompted the initiation of culling operations in some instances, such as Orca or Killer whales in Iceland and Greenland and various toothed whales in Japan. Some resource managers maintain that culling of cetaceans and some other marine mammals will improve fisheries yields. This argument is considered simplistic and invalid by fisheries and marine mammal scientists due to the complexity of the marine ecosystem.
Global climate change: As the evidence accumulates that global climate changes is causing severe perturbations in ocean currents, whales, like other marine species, are likely to be affected. Global warming is already causing polar ice to melt. This could destabilize the ecology of the Arctic and Antarctic feeding grounds of many large whales and acutely jeopardize the bowhead, narwhal, and beluga, which live in Arctic waters year-round. Changes in ocean temperature could also shift the distribution of plankton and fish species, disrupting the feeding patterns of cetaceans that consume them.
Depletion of whales' food supply: Antarctic krill: There are worrying indications that climate change is also resulting in a drop in the population level of krill. A reduction in supplies of this small, shrimplike crustacean, a key source of food for many marine species, could now be the greatest threat facing Southern Hemisphere baleen whales. A dramatic decrease in krill could be catastrophic, especially for the endangered blue whale. There is evidence that krill is already in short supply at least in parts of the Southern Ocean, with seals, penguins and albatrosses being unable to rear as many young in the 1990s as they did before. The supply of Antarctic krill is crucial to the whole Southern Hemisphere marine food chain, including all the whales that migrate to the Antarctic to feed. It appears that the main food supply for krill consists of algae which overwinter in the sea ice and are released and begin reproducing when the ice melts, so there is very high productivity close to the ice in summer.
WWF's CONSERVATION AND RESEARCH ACTIVITIES
WWF is developing an ambitious conservation programme for endangered whale species and populations. WWF's long term vision for whales is for: