Commercial whale hunters are certain to be upset by a new study from two US scientists. Based on an examination of whale genes, the researchers conclude that these mammals will not repopulate fast enough to overturn an international whaling ban anytime soon, but other scientists are skeptical of the conclusion.
When Europeans first sailed to North America more than 300 years ago, they marveled at the large numbers of whales they could see. But whale hunters in search of whale oil, bone, and other parts have reduced their numbers so much that the International Whaling Commission imposed a commercial hunting moratorium in 1986 to prevent extinction.
Under commission guidelines, hunting can resume when the various whale populations such as the humpback, fin, and minke return to 54 percent of their original size. But what were those sizes?
The International Whaling Commission has established estimates based on historical records, like whalers' logbooks. But Stanford University marine biologist Stephen Palumbi says those estimates are 10 times too low and could have negative repercussions for whale regeneration in the North Atlantic.
"Their normal population size is not 20,000, but 240,000 in the case of humpback whales. So our conservation targets for that species should be geared to the natural population levels that that species has always had, and those targets should then be dramatically increased," said Mr. Plaumbi.
To reconstruct whale history, Mr. Palumbi and a colleague analyzed the genetic material DNA in humpback, fin, and minke whales. In a paper in the journal Science, they note wide variations in the genetic makeup of each species. Scientists say the greater the genetic diversity, the greater the original population.
Mr. Palumbi assumes that whaling is what decimated the mammals. He says that based on his genetic estimate, the international whaling moratorium should continue for a long time.
Mr. Palumbi said, "We are looking at still needing to continue those protections well into the next century if the genetic data are taken into account, whereas based on whale log books, that population is just about ready to exploit."
But many scientists object to his whale census. One of them, University of California whale population geneticist Per Palsboll, concedes that such large numbers of the animals might have lived eons ago in a very different climate. But he points out that the climate of the last few centuries "the whaling age" might not support as many.
"So using that population size as a standard yardstick to which we need to recover population today becomes a little bit tricky because it might be impossible, even under the best conditions, because we have a different climatic regime today," said Mr. Palsboll.
Other researchers question Mr. Palumbi's assumptions about rates for gene mutations, which contribute to DNA diversity. Even minor rate changes in whales, which are scientifically plausible, could throw his numbers off considerably.
Still others are not about to abandon whale population estimates based on old logbooks. U.S. government whale biologist Phillip Clapham in Woods Hole, Massachusetts says old time whalers kept fairly accurate slaughter records.
"There is no question they are realistic. Palumbi just doesn't understand it. There was no incentive at all for whalers to lie about their catches. And if you reconcile the catch record with independent records of oil production, they match," said Mr. Clapham.
Stephen Palumbi acknowledges that his genetic data might be off and plans to study the diversity and mutation rates of other whale genes for comparison. He also concedes that his data cannot pinpoint the era of his estimated large whale populations. But he says it is reasonable to assume whaling caused their sharp decrease.
"Genetics can't tell you that that was the cause," Mr. Palumbi said. "Genetics can just point out that there was a large population, and now there is quite a small population. The obvious culprit is, of course, whaling."
In the meantime, 49 of 51 International Whaling Commission member countries continue to honor the hunting moratorium. Norway and Japan are the two exceptions. But all are monitoring whale stocks so they can determine when to remove the ban.
