The International Union for the Conservation of Nature (IUCN) which draws up the Red List of Threatened Species, says the situation is probably even worse because more than half of cetaceans - 44 species - are classed as Data Deficient which means that not enough is known about them to make an assessment.

South American franciscana (top) and finless porpoise (bottom) are both now Vulnerable. [Agencies]

It is the smaller coastal cetaceans who are facing the greatest threat, mainly from fishing boats.

The Irrawaddy dolphin (Orcaella brevirostris), the finless porpoise (Neophocaena phocaenoides) and the South American franciscana (Pontoporia blainvillei), are now all listed as Vulnerable, meaning they are threatened with extinction.

The study says the vaquita (Phocoena sinus), a porpoise in the Gulf of California, Mexico is likely to be the next cetacean species to go extinct. Already listed as Critically Endangered, an estimated 15 per cent of its dwindling population is killed in gillnets every year, leaving only about 150 alive in the wild.

The Yangtze River dolphin or baiji (Lipotes vexillifer) was classified as Critically Endangered, Possibly Extinct on last year's IUCN Red List and it is feared that the vaquita will follow the same path.

Randall Reeves, chair of the Cetacean Specialist Group of the IUCN Species Survival Commission, who led the Red List assessment, said: "Too many of these small coastal cetaceans end up as bycatch in fisheries. This remains the main threat to them and it is only going to get worse."

And Jean-Christophe Vié, deputy head of IUCN's Species Programme, said: "River dolphins are one of the most threatened cetacean categories, mainly because they are locked in competition with humans for dwindling freshwater resources."

But there is better news for at least some of the larger species. The humpback whale (Megaptera novaeangliae) has moved from Vulnerable to Least Concern, meaning it is at low risk of extinction, although two subpopulations are Endangered. And the southern right whale (Eubalaena australis) has also moved to Least Concern.

"Humpbacks and southern right whales are making a comeback in much of their range mainly because they have been protected from commercial hunting. This is a great conservation success and clearly shows what needs to be done to ensure these ocean giants survive," said Reeves.

The blue whale (Balaenoptera musculus), fin whale (Balaenoptera physalus) and sei whale (Balaenoptera borealis) all remain listed as Endangered, pending more evidence of recovery.

The study says whales are under threat in many areas from ship strikes, entanglement in fishing gear, habitat deterioration, declining prey and noise disturbance.

With the decline in whale hunting over the last few decades, accidental killing in fishing gear has become the main threat to cetaceans.

Besides the vaquita, the Black Sea harbour porpoise (Phocoena phocoena relicta), which moved from Vulnerable to Endangered, the North Atlantic right whale (Eubalaena glacialis) and the western gray whale (Eschrichtius robustus), already listed as Endangered and Critically Endangered respectively, are among the cetaceans most at risk from this threat.

"Disentanglement programmes to release whales captured in fishing gear, already carried out in the United States, New Zealand and Australia, help some individuals survive," says Bill Perrin, chair of the IUCN Cetacean Red List Authority.

"However, areas of critical habitat need to be closed to certain types of fishing, at least seasonally, to ensure the survival of some species."

The IUCN said increasing use of military sonar also posed a severe threat to whales and particularly deep-diving beaked whales and other cetaceans like the melon-headed whale. Mass strandings of these species have occurred more often in the last 30 years.

"Large parts of the oceans are now filled with human-generated noise, not only from military sonar but also from seismic surveys and shipping. This noise undoubtedly affects many cetaceans, in some cases leading to their death," says Jan Schipper, Conservation International and IUCN global mammal assessment director.

"It may not always kill whales and dolphins, but it affects their ability to communicate and it can drive them away, at least temporarily, from their feeding grounds."

Climate change was also beginning to affect whales because it was bringing exposure to new diseases, inter-species competition and changes in prey populations. As an example the Antarctic great whales were dependent on krill for food but this was alongside rising water temperatures.

Julia Marton-Lefèvre, IUCN director general, said: "To save whales for future generations, we need to work closely with the fishing industry, the military and offshore enterprises including shippers and oil developers - and we need to fight climate change."

(China Daily via Agencies?August 12, 2008)