Consider a world without whales.

Then consider how close we got to becoming such a world.

In 1966, scientists reported only a few thousand humpback whales left in the world's oceans.

That's the year an international ban on hunting humpbacks took effect.

Now, four decades later, the International Union for Conservation of Nature says there are at least 60,000 humpbacks.

That's why the IUCN announced this week that it's removing the humpback from its "vulnerable" list, in its annual report on the health of whale, dolphin and porpoise species.

The IUCN also says the minke whale and the southern right whale are no longer threatened with extinction.

"Humpbacks and southern right whales are making a comeback in much of their range mainly because they have been protected from commercial hunting," said IUCN marine mammal expert Randall Reeves, in an Associated Press report. "This is a great conservation success, and (it) clearly shows what needs to be done to ensure these ocean giants survive."

But not all cetaceans are doing as well as the humpback.

("Cetacean" is the collective term for whale, dolphin and porpoise species.)

The IUCN says the northern right whale is still in danger of extinction, along with the fin whale, the sei whale and the biggest whale of all, the blue whale.

And several dolphin and porpoise species are in grave danger of disappearing as well, including the Irrawaddy dolphin, the finless propose, the franciscana dolphin, the Chinese white dolphin and the vaquita, a porpoise that lives in the Gulf of California.

Scientists estimate there are only 150 vaquitas left.

One of the biggest threats to dolphins and porpoises is fishnets.

As you probably know, dolphins, porpoises and whales are mammals. That means they have to surface to breathe in air.

If they get stuck underwater in nets and can't surface, they drown.

Water pollution, collisions with ships and noise pollution from sonar are also ongoing concerns for all cetacean species.

So is global warming.

Iceland, Japan and Norway continue to hunt minke whales commercially, even though an international moratorium on whale-hunting went into effect in 1986.

But those nations are only allowed to kill a certain number of whales.

A Norwegian official says the IUCN's report proves that restrictions on commercial whaling should be relaxed.

"We would hope that some of the decisions might be reconsidered," said Halvard Johansen, deputy director general of the Norwegian Fisheries Ministry, in an interview with Reuters news service.

But the environmental group Greenpeace says the whaling ban still needs to be enforced.

"While some species of whales have started to recover, none of them are back to the levels they had before industrial whaling started," said Greenpeace spokesperson Frode Pleym. "This report should not be an excuse to hunt these species back to an endangered level again.

"Commercial whaling is unsustainable," Pleym continued, meaning that whales cannot reproduce fast enough to survive unlimited whaling. "It doesn't make any sense in economic terms. And it should stop."