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Stanford Report, August 6, 2003

Whale populations are too low to resume commercial hunting, geneticists find


Scientists have vastly underestimated the number of humpbacks and other great whales that inhabited the North Atlantic Ocean before the advent of whaling, according to geneticists from Stanford and Harvard Universities. Their findings, published in the journal Science, could represent a major setback for countries that advocate lifting a 17-year moratorium on commercial whaling established by the London-based International Whaling Commission (IWC).

The worldwide population of humpback whales, estimated at 20,000 may have been as high as 1.5 million before the advent of 19th-century commercial whaling, according to a new genetics srudy by researchers from Stanford and Harvard Universities. Photo: Dr. Louis M Herman / NOAA

"The IWC is the main organization that regulates whaling, and its policies allow for the resumption of commercial hunting when populations reach a little more than half of their historic numbers," said Stephen R. Palumbi, a professor of biological sciences at Stanford and co-author of the July 25 Science study. The problem, he noted, is that the IWC bases its historic estimates on unconfirmed whaling records dating back to the mid-1800s.

"It is well known that hunting dramatically reduced all baleen whale populations, yet reliable estimates of former whale abundances are elusive," wrote Palumbi and Harvard graduate student Joe Roman, lead author of the study. "Whaling logbooks provide clues, but may be incomplete, intentionally underreported or fail to consider hunting loss."

Genetics surprise

To assess the accuracy of historic whaling records, Roman and Palumbi turned to the science of population genetics.

"Our study marks the first attempt to use genetics rather than whaling records to confirm the number of whales that used to exist," said Palumbi, whose lab is based at Stanford's Hopkins Marine Station. "The genetics of populations has within it information about the past. If you can read the amount of genetic variation -- the difference in DNA from one individual whale to another -- and calibrate that, then you can estimate the historic size of the population."

In their study, Roman and Palumbi focused on the genetics of humpback, fin and minke whales -- three species decimated in the mid-19th and early-20th centuries by the demand for whale oil (for lamps, candles, soaps and perfumes), baleen (for whips, corsets and other devices) and meat. Although humpbacks, fins and minkes are found in many oceans, the researchers restricted their DNA analysis to the North Atlantic -- with surprising results.

"The genetics we've done of whales in the North Atlantic says that, before whaling, there were a total of 800,000 to 900,000 humpback, fin and minke whales -- far greater numbers than anybody ever thought," Palumbi said.

Take humpback whales, for example. According to the IWC, the current population of North Atlantic humpbacks is about 10,000, compared to its historic high of 20,000 -- a figure based on old whaling records. But after comparing DNA samples from 188 humpbacks, Roman and Palumbi concluded that the historic population in the North Atlantic may have been 10 times greater than the IWC estimate.

"A small population tends to weed out all of its genetic differences through inbreeding," Palumbi observed. "A large population, by contrast, should have a lot more genetic variation. Our study shows that humpback whales today actually have about 10 times more genetic variation than would be expected from the whaling logbook estimates. That tells us that, sometime in the past, the population of humpbacks was pretty big -- and in fact our calculation for the North Atlantic suggests that the historic size of that population was about 240,000 animals."

Using these results, Palumbi estimated that the worldwide humpback population could have been as high as 1.5 million -- more than 10 times the IWC's global historical estimate of 100,000. Exactly when the population reached that size will have to be determined in future genetic expeditions, he added: "We know from the genetics that there were many, many humpback whales in the ocean, but when those numbers started to drop is something we haven't been able to pinpoint yet."

Palumbi pointed out that, although the humpback population today is small because of whaling, "the genetic signal persists in that population for a long time, so we're really reading the past signal in the current population. And that past signal is far higher than it should be if there were only 20,000 whales in the North Atlantic."

An analysis of fin whale DNA yielded similar results. According to historic whaling records, about 40,000 fin whales once inhabited the North Atlantic. Current IWC estimates place today's fin whale population at 56,000, which would be an all-time high. But a genetic comparison of 235 fin whales by Roman and Palumbi revealed that the actual pre-whaling population was probably about 360,000 -- again, roughly 10 times higher than the IWC's historical estimate.

"Somehow we have to reconcile those numbers," Palumbi added. "That's going to require going back and looking at the whaling records. Are they complete? Have there ever been large hunts of whales that weren't recorded? These are things that we have to find out."

A humpback whale (Megaptera novaeangliae) breaches off the coast of Hawaii. Found in all the oceans, humpback whales reach sexual maturity at around age 12 and can grow to 48 feet long. PHOTO: Stan Butler/NOAA

Conservation conundrum

For Palumbi, reconciling those numbers is not an esoteric pursuit but rather an essential component of whale conservation for the 21st century. "Several countries would like to re-start commercial whaling," he noted. "The question is, when is a population large enough to allow whaling to begin? That depends upon how many whales there used to be before whaling wiped them out."

In 1986, the IWC declared a worldwide moratorium on commercial whaling -- a position respected by all 51 IWC member-nations except Norway, which openly permits the annual sale and slaughter of about 550 North Atlantic minke whales, and Japan, which allows certain species in Antarctica and the North Pacific to be harvested for "scientific purposes." Under IWC guidelines, a majority of members could lift the moratorium and allow other countries to hunt whales in regions where the population has reached 54 percent of its original carrying capacity.

"This is a real conundrum," Palumbi said. "Humpback whales, for example, were thought to have numbered about 20,000 in the North Atlantic, and we're up to about 10,000 now, so at that rate, the IWC could allow countries to start killing humpbacks within the next decade. But if the historic population was really 240,000, as the genetics suggests, then we wouldn't be able to start whaling for another 70 to 100 years."

Conservationists also are concerned about the fate of minke whales, whose meat is prized in Norway, Japan and elsewhere. In their Science report, Roman and Palumbi analyzed DNA samples from 87 minke whales and concluded that the pre-whaling North Atlantic minke population was at least 265,000 -- roughly twice the number of minkes that inhabit the North Atlantic today, according to the IWC.

Phantom knowledge

"In light of our findings," Roman and Palumbi concluded, "current populations of humpback or fin whales are far from harvestable. Minke whales are closer to genetically defined population limits, and hunting decisions regarding them must be based on other data."

Unfortunately, Palumbi added, much of the scientific data on the state of the oceans -- past and present -- has proved incorrect: "We forgot how many whales there were, or we never really knew. We could call this presumption of information 'phantom knowledge.'"

Many ocean ecosystems are in serious decline, he noted, pointing to a well-publicized study in the May 15 issue of the journal Nature, which found that approximately 90 percent the oceans' stocks of tuna, cod and other large predatory fish have been depleted by commercial fishing. Whales are also large predators, and their demise has had a significant impact on ocean ecosystems, observed marine biologist Boris Worm, co-author of the Nature study.

"One of the few collective actions of mankind was to save the great whales from extinction through a worldwide ban on commercial whaling," said Worm, a researcher with the Institute of Marine Sciences at Kiel University in Germany. "This new paper by Roman and Palumbi shows us that, despite recent population increases, we are still far away from our goal of allowing whales to recover fully from relentless exploitation."

The loss of more than 800,000 humpback, fin and minke whales in the North Atlantic is likely to have altered the entire web of life in that ocean, added James Estes, a research scientist with the U.S. Geological Survey and adjunct professor of biology at the University of California-Santa Cruz: "Clearly, the disappearance of the great whale was not an isolated event."

Not only are baleen whales major consumers of krill and small fish, he explained, but when they die, their massive carcasses sink to the bottom and provide vital nutrition for a wide variety of creatures on the sea floor. For example, an adult humpback can reach 50 feet in length and weigh up to 40 tons. Multiply that by 240,000 whales, and the impact of the loss becomes apparent.

"Sharks and killer whales are known to prey upon humpback whales, and their demise likely had a big effect on those predators as well," Estes noted. "So the implications of the Roman-Palumbi study for ocean conservation are startling. It could entirely redefine our recovery criteria for whales."

Watching versus whaling

Instead of catering to commercial whaling interests, a number of scientists and policymakers have urged the IWC to encourage the development of commercial whale watching -- an industry that generates more than $1 billion in annual revenues worldwide, according to a June 2003 report by the conservation group WWF (World Wildlife Fund).

"The IWC is a whaling organization. It's not a conservation organization, although the last IWC session did vote to include a new committee on conservation -- a major step for them. But the IWC's main goal is to re-start whaling as soon as whale populations have come back to levels it considers safe," Palumbi observed.

"Our conception of how the oceans and their ecosystems were put together probably needs to change, and genetics is one of the new tools that allows us to do that. We are the stewards of these magnificent creatures, and knowing something about their history is crucial in order to bring their populations back."

The Science study was supported by a Mia J. Tegner Memorial Research Grant in Marine Environmental History and Historical Marine Ecology from the Marine Conservation Biology Institute; the National Science Foundation; and the Pew Charitable Trusts.