A humpback whale jumps out of the waters off Hawaii in this photo, date unknown. (NOAA Fisheries/Associated Press)

The humpback whale, for four decades the poster child of the conservation movement, is no longer considered a high risk for extinction, a leading environmental group said Tuesday.

The International Union for Conservation of Nature, which each year produces a Red List of threatened species, has moved the humpback whale's status from vulnerable to least concern. The Switzerland-based IUCN did the same for the southern right whale.

"Humpbacks and southern right whales are making a comeback in much of their range mainly because they have been protected from commercial hunting," said Randall Reeves, an expert with IUCN Species Survival Commission specializing in cetaceans, the group of aquatic mammals that includes whales, dolphins and porpoises.

"This is a great conservation success and clearly shows what needs to be done to ensure these ocean giants survive," he said in a statement.

The humpback whale population dropped to the "low thousands" before it was banned from commercial hunts in 1966. Its population has now risen to at least 60,000, according to Bill Perrin, the chair of the IUCN Cetacean Red List Authority.

The IUCN said many smaller cetaceans are still under threat, however, with more than a quarter still considered threatened and two species and 12 subpopulations listed as critically endangered.

The vaquita, a porpoise native to the Gulf of California off the coast of Mexico, is most likely the next species to go extinct, the group said. Only an estimated 150 of the porpoises are alive in the wild and fishing gillnets are killing about 15 per cent of the population every year.

"Too many of these small coastal cetaceans end up as bycatch in fisheries," said Reeves. "This remains the main threat to them and it is only going to get worse."

The IUCN Red List includes around 41,000 species and subspecies from around the world.

The review is part of a larger survey of the world's mammals, due to be released in October at the IUCN World Conservation Congress in Barcelona.

With files from the Associated Press