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World's Oceans once Teemed with Whales

by Steve Connor, BBC Science Editor, Washington

Scientists have seriously underestimated the number of whales that lived before industrial-scale hunting began

20 February 2005.

The oceans once teemed with many more now endangered marine mammals than previously thought, new genetic studies of whales suggest.

So few whales seen today
So few whales seen these days (Photo: Kaikoura, South Island)

Whalemeat samples bought from a Japanese sushi market and analysed by scientists indicate that experts have seriously underestimated the size of the populations that roamed the seas before industrial- scale hunting began more than a century ago. The numbers of some species may have been 10 times greater than previously calculated.

The findings refute suggestions by whaling nations such as Japan that a resumption of hunting is justified by the increase of many whale populations beyond their natural size, the researchers said this weekend.

The latest information, reported to the annual meeting of the American Association for the Advancement of Science in Washington DC, is crucial to discussions within the International Whaling Commission (IWC) where some experts are suggesting that hunting minke whales could be resumed because the recent rise in their numbers is unprecedented and is hampering recovery of other whales.

Steve Palumbi, a marine biologist at Stanford University in California, found that the genetic diversity of whales is so large that it can only mean that past population sizes were much bigger than anyone had estimated.

"Genetic variation is related to long-term population size," Dr Palumbi said. "The International Whaling Commission estimates that past population sizes of humpback whales numbered no more than 115,000 before whaling."

His analysis of humpback whale DNA, however, led him to estimate that the past population size of breeding females alone must have been between 125,000 and 250,000 individuals

"Mature breeding females make up about one sixth to one eighth of a whale population, so these numbers suggest a global humpback whale population size [in the past] of about 750,000 to 2 million animals," he said.

Whales sometimes seen
Whales are sometimes seen (Photo: Puerto Vallarta)

Dr Palumbi also discovered that the Antarctic population of minke whales is now the longest surviving whale population on earth, and was also one of the largest - many times larger than previous estimates for the IWC.

Genetic variation is created by mutations accumulating over many generations. The bigger the population became historically, and the longer it has existed, the bigger the diversity of the DNA within an existing whale population.

"Best estimates suggest past abundance was about 10 times higher than thought for humpback and fin whales, and was about three times higher for minke whales," Dr Palumbi said.

The study also attempted to find out when the dramatic decline in whale numbers occurred. Dr Palumbi said that it was relatively recent - thousands rather than millions of years ago, and probably later than the last Ice Age about 10,000 years ago.

The decline affected many species worldwide. "We know of one factor that accounts for these patterns - historic whaling," Dr Palumbi said.

"Whales have shown remarkable resilience to cataclysmic events, until the last one, which is us.
"Ice ages, sea level change and even loss of local food sources did not interrupt their lives."

Separate research presented to the conference showed that whales sing to one another over hundreds of miles and use their songs to navigate across oceans.

Underwater microphones developed to monitor Soviet submarines have detected cohorts of humpback whales travelling thousands of miles as a group, singing to each other as they go, said Christopher Clark of Cornell University in Ithaca, New York.

"Whales will aim directly at a seamount that is 300 miles away, then once they reach it, change course and head to a new feature," Dr Clark said. "It is as if they are slaloming from one geographic feature to the next. They must have acoustic memories analogous to our visual memories."


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