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Last Updated: Thursday, 31 May 2007, 19:57 GMT 20:57 UK
Blue whales 'making a comeback'
By Richard Black
Environment correspondent, BBC News website, Anchorage, Alaska

Blue whale (Science Photo Library)
Marine scientists are encouraged by the gentle giants' progress
The blue whale, possibly the largest animal ever to live on Earth, is making a comeback, scientists have said.

They have collated data showing that the number of marine mammals in the Southern Hemisphere has increased from a few hundred to a few thousand.

Before the commercial hunting era, there would have been hundreds of thousands in the oceans.

The findings were presented at the International Whaling Commission's (IWC) annual meeting.

Numbers of other large species such as fin whales and humpbacks are also rising in many parts of the world.

"The most recent data is really encouraging," said the IWC's head of science, Greg Donovan.

"Blue whales have now been increasing by about 7-8% per year for the last 10 years at least, for which we have good data.

Blue whale graphic (BBC)

"The abundance is still very low; it's about 2,300 for the whole Southern Hemisphere so it's a tiny fraction of what it used to be, but it's good news they're increasing."

There is less data available for the Northern Hemisphere, but off the Icelandic coast a recovery has also been noted.

The IWC's "guesstimate" is that globally, numbers are currently about 4,500.

Top target

Blue whales are true leviathans, growing up to 30m in length and weighing up to 190 tonnes.

Before industrial-scale commercial hunting began in earnest about a century ago, there were thought to be 150,000-200,000 in the oceans.

Archive image of whale hunting vessel (Getty Images)
Commercial whalers caught thousands of blue whales each year

As factory ships and efficient harpoons multiplied, the blue's size made it the favoured species, as vast quantities of oil could be extracted from its blubber.

The 1930-1931 season alone saw about 30,000 prised from the oceans.

Protection arrived in the 1960s; but with numbers so low, it was doubtful whether the species could survive.

For now, it has survived, with its extraordinary capacity to communicate acoustically over distances of thousands of kilometres meaning it can find mates even when so few remain.

Renewed threat?

Global protection from hunting for the second largest species, the fin, and the whale-watcher's favourite, the humpback, have also led to populations rising in several parts of the oceans.

But that can bring mixed benefits. There have been rumours over the last six months that scientists advising the organisation which decides threat categories for animals, the World Conservation Union (IUCN), are contemplating moving humpbacks from their current Vulnerable status to a less threatened category.

As numbers grow, so does the likelihood that a species will be hunted.

For the moment, catches of these giant creatures remain low. Over the next 12 months, hunters from Japan, Greenland, Iceland and the Caribbean will target 78 fins and 54 humpbacks, and nobody is suggesting catching blue whales again.

Dr Donovan sees climate change as potentially the biggest long-term threat.

"We don't know whether climate change is going to be a big problem for whales, but it could be," he said.

"Blues feed very close to the ice edge, and if there's less ice then it could affect them. But it could be that the opposite will happen, we really don't know at the moment."

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