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13 Jul 06
Rare Whales Can Live to Nearly 200, Eye Tissue Reveals
John Roach for National Geographic News
Scientists have looked into the eyes of rare bowhead whales and learned that some of them can outlive humans by generations—with at least one male pushing 200 years old.
"About 5 percent of the population is over a hundred years old and in some cases 160 to 180 years old," said Jeffrey Bada, a marine chemist at the Scripps Institution of Oceanography in La Jolla, California.
"They are truly aged animals, perhaps the most aged animals on Earth," he continued.
Bowheads, also known as Greenland right whales, are baleen whales, meaning that instead of teeth they have bonelike plates that they use to strain food from gulps of water. The whales live in the Arctic (virtual world: Arctic interactive feature). Adults can reach 60 feet (18 meters) long and weigh more than a hundred tons (89 metric tons).
In the 1990s Craig George, a wildlife biologist with the Alaska Department of Wildlife Management in Barrow, was involved in a bowhead whale survey program for the International Whaling Commission. The regulatory body banned commercial whaling of bowheads in 1946.
Inupiat Eskimos, however, have traditionally hunted the whales and are allowed to kill a certain number each year for food and oil. George examined several whales killed during an annual Inupiat hunt and found stone harpoons imbedded in their flesh.
According to the Scripps Institution's Bada, "Stone harpoons rapidly disappeared when Europeans went into the Arctic. … That was around 1860, 1870." "All of a sudden we had whales killed in the 1990s with stone harpoons in them, suggesting they may be a hundred years old."
George contacted Bada, who had done pioneering research a decade earlier showing that bowheads can reach a hundred years or older. At the time, Bada's work had been dismissed as nonsense.
"Most whale species were thought to live half that length of time," said Bruce Mate, a whale expert and director of the marine-mammal program at Oregon State University in Newport. Based on tissue samples George sent, Bada found that most of the whales were between 20 and 60 when they died. But five males were at least 100, and one was pushing 200.
Bada's age-determining technique involves amino acids, the building blocks of proteins found in all living animals. His method takes advantage of a unique characteristic of amino acids to determine the ages of animals, including whales.
"What's interesting about amino acids is they have a property called handedness. They can occur in either a left- or right-handed form," he said. When animals create new tissue via active metabolism, they create only left-handed amino acids. But when active metabolism stops—most often when an animal dies—a process called racemization takes over and creates an equilibrium. The process converts left-handed amino acids into right-handed amino acids until there are equal amounts of both, Bada explains.
Certain tissues, such as teeth and the lens of the eye, are isolated from active metabolism early in life, allowing the conversion to begin sooner, while the animal is alive.
"It turns out the proteins in the nucleus of the eye lens are probably the oldest proteins in the body," Bada said. "They are synthesized [before birth] and are never ever again involved in active metabolism."
With increasing age, therefore, more and more right-handed amino acids accumulate in the lens of the eye. Once scientists know the rate of this process, they can estimate the age of an animal by analyzing the proportion of the lens's right-handed amino acids.
Mate, of Oregon State, says George and Bada's findings immediately altered how scientists think about bowhead population dynamics.
For example, he says, whale biologists now believe bowhead females go through menopause. "There are locations in the high Arctic where we see very large animals without calves. We think these are old females who are no longer reproductive," he said.
Mate adds that the bowhead whales may be unique in their longevity. There is no indication that temperate and subtropical large whale species live as long as bowheads.
But Bada, of Scripps, says the jury is still out on the uniqueness of bowhead age. "Most other whale populations have been so heavily exploited we may not have an accurate picture of these animals, as far as natural age structure," he said.
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