Study Questions Comeback of Gray Whale
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Starving Whales Point to Depleted Oceans [
Study Questions Comeback of Gray Whale
The Associated Press
Tuesday 11 September 2007
Palo Alto, California - One of the great success stories of the ocean, the return of the Pacific gray whale, may have been based on a miscalculation, scientists reported Monday in a study based on whale genetics.
What was assumed to be a thriving whale population actually is at times starving from a dwindling food supply, said study co-author Stephen Palumbi, a Stanford University marine sciences professor. And global warming is a chief suspect.
Scientists may have underestimated the historical number of gray whales from Mexico to Alaska, according to the study published Monday in the Proceedings of the National Academy of Sciences. And that may have led to a misdiagnosis of what is behind surprising die-offs over the past few years and the appearance of many so-called "skinny" whales.
Earlier this month the National Marine Fisheries Service reported that at least 10 percent of gray whales returning to one of their four main calving and breeding lagoons off Baja California showed signs of being underfed. Some of the whales even had bony shoulderblades.
"This is a hint of a problem," Palumbi said. "Our antennas should be up. Our antennas should be asking if the ocean is capable of supporting life the way it used to."
The study concludes that the original Pacific gray whale population hundreds of years ago may have been far higher than currently thought - closer to 100,000 whales than conventional estimates of 20,000 to 30,000.
The scientists base that on how diverse the population of whales once was - information they gleaned by examining differences in the DNA of 40 whales. They studied 10 spots on the whale's genetic blueprint.
The diversity of genes in this group of whales indicates there had to be about 100,000 whales centuries ago, the scientists reported.
If the whale population was five times higher than originally thought, that makes recent problems with the whale look far worse.
Gray whales were the first marine mammal to bounce back and get off the endangered species list in 1994. Scientists had figured that a population of about 20,000 whales was normal, so in 1999-2000 when some whales started dying off, the experts figured it was just the result of the ocean reaching its normal "carrying capacity." There was just not enough room for more whales, so nature thinned out the herd, they figured.
But Palumbi said his genetic analysis shows the oceans were once more crowded with gray whales. He said anecdotal historical evidence supports that. One historical document claimed a count of 1,000 whales a day seen on the California coast.
French explorer Jean-Francois La Perouse sailed into Monterey Bay in the 1700s and complained "there were so many whales, that they stunk up the air with their breath," Palumbi said.
While some scientists said Palumbi's work makes sense, it left a nagging question for fisheries biologist Jeff Breiwick, who works on the gray whale census for the National Marine Mammal Laboratory in Seattle: What happened to the 80,000 gray whales for which there is no evidence?
Breiwick and others have used computer models and historical documents to estimate the level of whale hunting since the 1600s. To explain the extra whales living and then dying would have meant about three whales a day being killed for four centuries.
"Where's the evidence of that mortality?" asked Breiwick.
Palumbi said the answer is in Asia. The gray whales in his study are eastern Pacific gray whales. Western Pacific gray whales look identical and can only be identified by genetic tests, he said.
Palumbi figures that the 100,000 whales of centuries ago would includes both types of whales, and the massive decline can be explained by Asian whaling. The western gray whales number only in the hundreds and are on the precipice of extinction, he said.
Getting the eastern Pacific whales back to nearly 20,000 is "a great success story, don't get me wrong," Palumbi said. "It's not a success story that's finished yet."
If the whales aren't at their natural limit, then some other problem is harming them, Palumbi said. And that has to do with a food shortage and global warming, researchers theorize.
The gray whale relies on massive numbers of small crustaceans that live in the Arctic regions, Palumbi said. That food supply may have been cut because of warmer waters, he said.
National Marine Fisheries Services whale expert Stephen Swartz who is investigating the problem of the starving gray whales said earlier this month that the issue may be connected with global warming.
Frances Gulland, director of veterinary science at the Marine Mammal Center in Sausalito, Calif., examined some of the whales that died in the 2000 and agreed with Palumbi that the new estimates on past population indicate that something bad is happening now.
On the Web:
http://stanford.edu/group/Palumbi/PNAS
Starving Whales Point to Depleted Oceans
By Catherine Brahic
NewScientist.com
Tuesday 11 September 2007
Starvation may be impeding the recovery of the Pacific Gray whale population, say researchers.
The Gray whale population was thought to have recovered from commercial whaling, but now a new genetic study suggests the marine mammals once numbered between three and five times the 22,000 population estimated today.
If true, the findings could imply that the world's oceans are no longer able to support the same number of whales that they once could, says Stephen Palumbi of Stanford University in California, US, who led the study.
Previously, it had been thought that thin, starving whales - as have been observed recently in Mexico - were a consequence of the population exceeding its historical ecological limits, rather than the oceans running out of food.
Palumbi speculates that a depletion in the whales' natural prey in the oceans could be down to natural variation or the warming of waters due to climate change.
"Our results might be telling us that whales now face a new threat - from changes to the oceans that are limiting their recovery," says Palumbi. "Decades ago, whales were the first creatures to tell us that we were over-fishing the oceans. Maybe now they trying to tell us the oceans are in deeper trouble."
Genetic Mutations
Palumbi and his colleagues obtained DNA samples from 42 Gray whales Eschrichtius robustus, and sequenced it at 10 different points to see how much genetic variation there was between individuals. This gives scientists an idea of how large a population once was.
"Genetic variation builds up in populations because of random mutations," explains Palumbi. The larger the population, the more random mutations occur in individual whales.
"In a small population, inbreeding tends to strip the variation away," he adds. It takes a long time for that to happen - the rule of thumb is that it takes at least 10,000 generations to strip away the variation of a population that originally comprised 10,000 individuals.
From the samples, the researchers determined that the Gray whale populations would have averaged between 78,000 and 118,000 over the past tens of thousands of years - rather than the current estimated population of 22,000.
Most of the existing population roams the eastern Pacific - there are only about 100 Gray whales left in the western region, making them some of the most endangered whales on the planet.
However, even if historically, the whales were evenly distributed between the American and Asian Pacific coasts, with 48,000 on either side on average, this would still mean that the current eastern Gray whale population is now half of what it was.
Malnourished and Emaciated
"It might be that the eastern Gray whales are on their way to recovery, in which case our study would suggest that we can expect them to keep growing," Palumbi told New Scientist. But in April 2007, the conservation group Earthwatch reported that eastern Gray whales were arriving at their breeding ground in Mexico malnourished and emaciated.
For Palumbi, the logical conclusion is that the oceans are no longer able to feed as many Gray whales as they once did. He says there could be any number of reasons for this, ranging from natural variation of the ocean's food supply, to human effects on the oceans. He also points to a 2006 study led by Jackie Grebmeier of the University of Tennessee at Knoxville, US, which showed that warming seas in the Arctic are displacing crustaceans on which the whales feed.
Depleted numbers of the whales, says Palumbi, is bad news for other species too. As Gray whales feed, they stir up sediment by "bulldozing" the ocean floor for food - this feeds animals throughout the marine food chain.
Palumbi and his colleagues have calculated that 96,000 Gray whales would have resuspended 12 times more sediment each year than the Yukon River, the biggest river in the Arctic.
For example, says Palumbi, "96,000 Gray whales would have helped feed over a million seabirds a year".
The researchers are recommending that the eastern Gray whales still be considered depleted and that the US Marine Mammal Protection Act should be amended to allow just 207 killings by humans a year, instead of the 417 currently allowed for the US.
Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0706056104)
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