The age of whales:
alienzoo.com
Research Suggests Bowhead Whales May Live for Centuries
TODAY'S SCENE
02/06/2001
Among the Inupiat of northern Alaska, they are a part of whaling lore, seemingly ageless bowhead whales that swim the frigid waters of the Chukchi Sea, eluding generation after generation of Eskimo hunter.
The first tangible evidence that lore might be something more came in the form of harpoon points extracted from whales harvested by Inupiat between the years 1978 and 1996. The points were made of stone and ivory, materials that had not been used by Native American whalers for more than 100 years.
How old were these whales?
In recent months, some surprising answers have emerged from studies conducted by scientists at Scripps Institute of Oceanography and elsewhere. Based on analyses of amino acids in whale eyes, researchers now estimate that some of the bowhead whales harvested by the Inupiat were well past a century in age. One male specimen was estimated to be 211 years old.
Such findings, if validated by further research, would establish whales - or at least bowheads - as the longest-living mammals on Earth. It would also mean rewriting and adding new chapters to what is known about cetacean biology.
"It's long been presumed that whales had life spans similar to humans, somewhere between 80 and 100 years," said Diana McIntyre, a member of the board of directors of the American Cetacean Society and research associate for the Natural History Museum in Los Angeles. "We went with that span based partly on what we knew about whale lives and reproduction, partly because we didn't have any hard data to suggest otherwise. It was an educated guess, though these findings suggest the truth may be something else altogether."
To be sure, Earth is home to a host of long-living organisms. Some bristlecone pines in the White Mountains of eastern California are estimated to be more than 5,000 years old. Giant tortoises can live well past 150 years. Some species of marine life, specifically orange roughy and Chilean sea bass, may reach the century mark. Certain parrots survive into their 70s; elephants and horses can live to be 60 years old. The oldest human on record is Jeanne Louise Calment, a French woman who died in 1997 at the age of 122.
The lives of whales, however, are not nearly so well-mapped.
"There was independent evidence that something fishy was going on with whales, things like scarring," said Jeffrey Bada, a biochemist at Scripps involved in the new research. "Some of these guys looked pretty damned ancient."
But pinning down a whale's age has long been problematic, said Lance Morgan, a researcher with the Marine Conservation Biology Institute in Redmond, Wash.
"Most whales live most of their lives in the open or deep sea, where they are obviously very difficult to observe and record for any length of time," Morgan said. "What we see of most whale lives is just those few seconds at the surface."
MARINE METHUSELAHS
The latest revelations about bowhead ages began with Craig George, a field biologist for Alaska's North Slope Borough Department of Wildlife Management. George began hearing stories in the early 1990s of old stone harpoon points found by Inupiat hunters inside the blubber of butchered whales.
George acquired the points, then compared them with ancient Eskimo harpoon heads collected by the Smithsonian Institution in Washington, D.C. The two sets matched. Moreover, the Eskimos had stopped using stone harpoon heads in the 18th century after being introduced to metal Yankee whaling tips.
Assuming the killed whales had been mature when first harpooned, the recovered stone points suggested to George and others that the animals had survived for more than a century. Indeed, the whales arguably died only because hunters had killed them. But proving that bowheads naturally lived for centuries would require more direct evidence.
There are several ways of estimating a whale's age. The maximum age of blue whales, the largest living animals on Earth, has been projected at approximately 110 years based upon counts of growth layers in the bony plugs of their eardrums.
Other whale aging techniques involve counting oscillations in stable carbon isotopes in whale baleen or bone. An isotope is any of two or more forms of an element with the same chemical properties but slightly different physical properties due to different numbers of neutrons in the atomic nucleus. You can think of it this way: Imagine two footballs identical in every way except that one is inflated to a slightly higher pressure, which causes it to perhaps bounce a bit higher.
In bowheads, the ratio of the isotopes in baleen changes annually as the whales migrate from region to region, feeding upon prey with different isotope profiles. The carbon in crustaceans, for example, eaten in the Bering Straits is slightly different from the carbon in crustaceans swimming in the Beaufort Sea. These varied profiles are laid down in the baleen as sort of a chronological chemical record of where the whale has been and when.
The technique, however, is limited to whales of relatively young age because baleen wears down with age, eradicating portions of the record.
Then George, the Alaskan biologist, read about research conducted by Bada at University of California, San Diego's Scripps Institution of Oceanography. Bada and colleagues had crafted a method in the late 1970s for dating marine mammals.
The process was based on amino acid racemization, a technique originally developed to assess the ages of fossilized bones, shells and wood. In particular, Bada looked at the presence of aspartic acid, an amino acid used to construct proteins in the metabolically inactive lenses of whales and other creatures.
Like other amino acids, aspartic acid occurs in one of two isomers or versions, called L and D forms. These are three-dimensional, molecular mirror images. (To visualize this concept, think of your right and left hand.) When originally produced, aspartic acid is laid down only in the L form, but over time it spontaneously switches back and forth at a known rate called racemization. As time passes, the ratio of L to D forms balances out. By measuring the ratio of L:D, it is possible to estimate how much time has passed since the first layer of aspartic acid was laid down.
Bada's eye lens racemization process was not widely embraced at the time he published his first paper in 1980. "At the time, the technology was brand new. It was chemistry. There were concerns about chemistry stepping into cetacean biology," said Bada.
Nonetheless, Bada's idea has been used successfully to date some whale and porpoise species, and it is occasionally used in human forensics.
To George, measuring racemization rates in bowheads sounded like a plausible way to date the whales with reasonable accuracy. Where other dating techniques were clearly inappropriate for bowheads - the whales lack bony earplugs, for example - they do have billiard ball-sized eyes with large lenses.
With access to the frozen remains of bowhead whales killed between 1978 and 1997, George sent two shipments of whale eyes to Bada for analysis - one shipment in 1996, the other the following year. Bada added other eyes he had retained from earlier experiments, bringing the total to 48 eyes available for analysis. Steve Brown, a high school biology teacher, performed the original dissections, extracting small core samples from each lens.
The actual process of racemization, using liquid chromatography, is extraordinarily precise, requiring rigid and frequent calibrations to measure L:D aspartic acid ratios, said Bada. The resulting age estimations are less so, with a margin of accuracy of 16 percent. Nonetheless, the range of numbers stunned scientists.
Four individuals (all males) among the 48 whales exceeded 100 years of age; with the oldest being a whopping 211.
"To find 10 percent of a sample being more than a century old is absolutely amazing," said Bada.
These findings, published by George, Bada and colleagues last year in the Canadian Journal of Zoology, have created something of a stir in the cetacean research community. Other researchers have subsequently launched whale dating projects of their own, including efforts to measure the decay of radioactive lead samples in bowhead bones and the presence of certain chemicals in bowhead skin. The latter project, by Cheryl Rosa at the University of Alaska, shoots small, retractable darts into living bowheads. The darts do not injure the whales. Rosa will then test the extracted plugs of whale skin for the presence of pentosidine, a chemical that accumulates with age.
WHALE TALES
While new studies go forward, scientists are beginning to grapple with what the new age estimates mean. Questions abound. Why do bowheads live so long? How does living so long change scientific understanding of whale biology?
Scientists have long presumed that whales evolved to great size because: they were little restrained by habitat; gravity was not much of a factor; and being big gave them a competitive advantage. Hugeness reduced likely predators.
Long life appears to naturally derive from size. "The energetic and skeletal requirements of attaining great body mass demand an extended life-span simply because growing large takes time," wrote George, Bada and the others in their paper. "Extended life-span is a shared life history trait of all large mammals."
But the discovery that bowheads appear to live so long has prompted more specific questions, said Morgan at the Marine Conservation Biology Institute. "Like: Are the older whales sexually reproductive?"
If so, then Morgan and others suggest a long life may be the species' way of perpetuating itself. In general, there are two basic survival strategies among animals. So-called "r-strategists" are creatures that live short lives in which they breed fast and furiously. Rodents, for example, counter their high mortality rate by reproducing in large numbers.
Conversely, "k-strategists" are animals that generate few offspring over long periods of time, such as pandas and elephants. Such an approach is a useful hedge in variable environments where living conditions may be poor for extended periods of time.
Early evidence suggests bowheads - and perhaps whales in general - are k-strategists. Bada said he has heard of one 90-year-old bowhead female that appeared to still be sexually reproductive. "Right now, there doesn't seem to be an upper age limit for these animals," he said.
However, it may turn out that bowheads do not routinely produce offspring in their second century of life, that in fact their reproductive lives are not especially long.
If that proves to be the case, Morgan said, then living a very long life may provide a different sort of survival benefit.
"Bowheads are reasonably social, intelligent animals. There are a lot of complexities about their social structure that we don't yet appreciate," Morgan said. "It may be that long-living individual whales accumulate knowledge about where to fish or how to avoid danger that is useful to the species as a whole. Perhaps they pass that knowledge on to younger members."
Whatever the specific reasons for bowhead longevity, their notably long life span is certain to alter perceptions of their scientific, environmental and cultural value.
At the turn of the 18th century, bowhead whales were on the verge of extinction due to widespread, unregulated commercial hunting. Today, they are protected but still considered to be a threatened species. International treaties permit only a handful of whales to be hunted annually by indigenous peoples like the Inupiat.
Barring renewed commercial hunting or a cataclysmic environmental disaster, bowheads living today may be around to answer the questions of our children, their children and generations beyond. |
