Patented harpoon pins down whale age
Collaboration with Eskimo hunters shores up theory on long-lived whales.
A 100-year-old patented harpoon point, a dead bowhead whale and a unique collaboration between traditional hunters and scientists has helped to prove the theory that northern-latitude whales are among the world's longest-lived mammals.
The discovery has particularly settled the doubts of Craig George, a biologist with the North Slope Borough Department of Wildlife Management in Barrow, Alaska, who first mooted the idea that these whales could be more than 200 years old. "We were a little frightened when we first published that," George says. But this latest finding, he says, adds to a collection of evidence that these whales can rack up 150 years or so. "I think it's time to believe it," he says.
The century-old harpoon fragment was found in May by an Eskimo whaling crew, which harvest the bowhead under a subsistence quota system monitored by the International Whaling Commission (IWC). The metal projectile can be traced back to an 1879 patent and a narrow window of time in which it was likely to have been fired, indicating that this whale was between 115-130 years old when it died.
The Eskimo hunters have a 30-year history of scientific cooperation and sharing of information with researchers at North Slope Borough. The relationship started out, says George, with an "extreme distrust of science" on the part of the Eskimo whalers because of a temporary IWC moratorium on subsistence hunting in 1977. Over time, the two groups began to collaborate, and the Eskimos shared their traditional knowledge in ways that improved the scientists' work, he says.
Their collaborations had previously turned up a handful of old lance fragments from whales that survived an initial attack. But most of those objects were made of stone and metal composites that could not be precisely dated.
Age estimates for whales are often determined by counting growth layers in their teeth or the wood-like plugs found in a whale's inner ear. But such methods have proved unreliable for some species, particularly with the older whales. And bowhead whales do not form solid ear plugs.
In 1999, a research team led by George analysed amino acids in the eye lenses of bowheads to determine their age. This showed up 42 successful age estimates, with most of the adults between 20 and 60 years old when they died. But five old whales were estimated at 91, 135, 159, 172 and a whopping 211 years old at the time of death1.
The results were considered highly controversial, in part because they did not square with population-based models: surveys of whale ages usually turn up very creatures over 100 years old.
Some researchers speculate that very few long-lived whales are found because of heavy population losses from an intense spate of commercial whaling between 1848 and 1915, which is thought to have reduced bowhead whale populations from more than 13,000 to fewer than 2,0002. This left few whales to produce offspring that would now be reaching their hundredth birthday.
Wait and see
"There hasn't been enough time for those really old populations to recover," says Stephen Palumbi, a marine biologist at Stanford University in California. "It will take 100 years of them growing well to see whether or not they begin to age and die when we think they will."
If the patented harpoon lends credence to the eye-lens technique for dating whales, then other whale species in the region also look to be centenarians. This year, researchers from Denmark and Greenland used the same eye-lens technique to estimate the age of narwhals, another Arctic species, and made one age estimate of 115 years3.
George is proud to point out that traditional Eskimo knowledge has said for centuries that bowheads live "two human lifetimes" — a statement that is now being corroborated by scientific study.
- George J. C., et al. Can. J. Zool., 77 . 571 - 580 (2007).
- Punt A. E., et al. J. Cetacean Res. Manage., 8 . 127 - 137 (2006).
- Garde E., Heide-Jørgensen M. P., Hansen S. H., Nachman G. & Forchhammer M. C. J. Mammal., 84 . 49 - 58 (2007).