Forty years ago conservationists feared that humpback whales were being hunted to extinction. Now numbers have returned to such a level that they have been taken off the danger list.

The latest count stands at 40,000 mature individuals, meaning that, for now at least, the humpback is safe from the threat of extinction.

Several other whales, such as the blue whale, the biggest animal on earth, and the sei and southern right whales, are also growing in number after similar scares.

The populations of several smaller species of whales and other cetaceans are still falling, however, and it is feared that some may be close to disappearing, according to the International Union for Conservation of Nature .

The vaquita, Phocoena sinus, a porpoise found in the Gulf of California, Mexico, is now thought to be down to the last 150 individuals and has been named by the union as the cetacean mostly likely to become extinct next.

The resurgence of the humpback, Megaptera novaeangliae, has nevertheless heartened conservationists. Whalers, especially the Soviet Union’s Antarctic whaling fleet, had caused devastation to the humpback population until hunting was halted in the Sixties.

The humpback had been described by the union as vulnerable to extinction, but it has now been reclassified as being of “least concern” – the lowest rating. Southern right whales, Eubalaena australis, have also been taken off the critical list after their population doubled from 7,500 in 1995. They, too, get a “least concern” rating in the union’s latest update of its Red List of threatened animals.

Researchers assessing the number of blue, sei and and fin whales concluded that their populations were also rising, but not enough for their endangered listing to be lifted.

Randall Reeves, a cetacean specialist for the union, believes that the improvement in the population of the bigger species of whales is mostly attributable to bans on hunting.

“Humpbacks and southern right whales are making a comeback in much of their range mainly because they have been protected from commercial hunting,” he said.

“This is a great conservation success and clearly shows what needs to be done to ensure these ocean giants survive. So long as commercial whaling isn’t happening, the increase should continue.”

The recovery has been going on for at least 20 years, he said, but it is a slow process because the large whales breed slowly.

He said that bowhead whales, Balaena mysticetus, found in the eastern Arctic, had taken a century to increase from the few hundred left by whalers to the 7,000 today. Bowheads can live for between 100 and 200 years, but do not breed until they are in their twenties and have one calf every three years.

Mr Reeves gave warning, however, that climate change could put an end to the resurgence by changing the availability of food, especially krill. Other species are still in decline, especially coastal and freshwater varieties.

Accidental death in fishing gear is now the most serious threat to cetaceans. Apart from the vaquita, those worst affected include the Black Sea harbour porpoise, Phocoena phocoena relicta, the North Atlantic right whale, Eubalaena glacialis, and the western grey whale, Eschrichtius robustus.

Bill Perrin, the chairman of the union’s Cetacean Red List Authority, said: “Disentanglement programmes to release whales captured in fishing gear help some individuals to survive. But areas of critical habitat need to be closed to certain types of fishing to ensure the survival of some species.”

Blowing bubbles, singing love songs

— Humpbacks blow bubbles to catch fish. By creating curtains of bubbles in the water they can trap shoals, which they then snap up

— Males sing for hours at a time and individual songs can last 20 minutes. It is believed to be mating behaviour Humpbacks have landed on small boats when breaching (soaring out of the water)

— They can swim 10,000 miles from their cold-water feeding grounds to tropical breeding territories

— Humpbacks grow to up to 16m and can weigh 40 tonnes. Calves are born more than 4m long and up to two tonnes in weight. They can live 50 years

— The whales usually dive for three to fifteen minutes. They can reach depths of about 150m

— Southern right whales got their name from whalers who considered them “the right whale” to hunt – slow, with large amounts of blubber, they floated when killed

— Tens of thousands were killed before the first world ban in 1937

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