Unlikely Partners in the Sea
Copyright Jessica Snyder Sachs, as first appeared in National Wildlife
Narwhals, among the Arctic
mammals most threatened by global warming, may help scientists track
temperature changes in otherwise inaccessible ocean depths
BIOLOGIST Kristin Laidre sits in her University of Washington office
overlooking Puget Sound's busy Portage Bay. With little prompting she lets her
mind drift to a much larger, colder bay some 2,500 miles to the northeast.
"What stands out about Baffin Bay," Laidre says, "is how you can fly for hours
over the dense ice, a landscape where you wouldn't expect a single living
thing, and then you look down and see a small lead, a tiny crack in the ice,
and there will be a narwhal."
On
the most memorable occasions, Laidre and her colleagues have watched what they
call the classic narwhal ménage à trois--two males crossing and rubbing their 6-
to 9-foot-long tusks above the head of a bobbing female. "It's quite
remarkable," Laidre says. Laidre has spent the past 10 years tagging, tracking
and studying the narwhal--the Arctic's most specialized, range-restricted and
northernmost whale. The narwhals of Baffin Bay account for 80 to 90 percent of
a world population of 50,000 to perhaps 80,000. A second group, of around
5,000, inhabits the northern part of Canada's Hudson Bay. An even smaller
population of unknown number lives east of Greenland.
The
narwhals that winter in the deep water of central Baffin Bay get there by
migrating thousands of miles from summering areas in the shallow bays and
fjords of the High Arctic. Despite the extreme cold and ice cover, winter is a
period of intense activity for this small, highly social whale. Winter is
mating as well as feeding season, a time when narwhals consume the vast
majority of their yearly diet.
On
a typical winter day, narwhals dive almost continually to graze on the
pitch-dark seafloor and there gorge on fatty, energy-rich Greenland halibut, or
"turbot." Many dives reach down to 5,000 feet and last some 30 minutes. At such
depths, narwhals are sustained solely by their highly oxygenated blood and
muscles, the deep-sea pressures having collapsed their lungs. When they surface
to breathe, as all whales must, narwhals zero in on small--sometimes
fleeting--cracks in the thick winter ice pack. Open water can suddenly freeze
during windless conditions and temperatures below minus 30 degrees F.
Come
April, the ice pack begins to loosen, signaling the narwhals to begin their
two-month-long northward migration. It's during this early spring window--when
the ice has loosened but has not yet turned to slush--that Laidre flies east
from Seattle to rendezvous with her longtime colleague, Mads Peter
Heide-Jorgensen of Greenland's Institute of Natural Resources. "Our work has
focused on gaining a fundamental understanding of how this animal uses its
ecosystem," Laidre says. "Only then can we begin to suggest ways that it can be
protected."
That
the narwhal remains so little studied stems directly from the difficulty and
expense of mounting research expeditions across Arctic seas, Heide-Jorgensen
says. "I'm sure a similar effort on almost any other creature would yield a lot
more data, but it's also gratifying to study an animal where every piece of
information you learn is worth its weight in gold."
For
starters, their team has documented the narwhals' faithfulness to their narrow
migratory routes. They've also reported the Baffin population's need to consume
some 880 tons of Greenland halibut daily each winter. Field observations and
autopsies on hunter-harvested whales have likewise confirmed that narwhals eat
surprisingly little during the milder summer months. "We don't know why, but narwhals
depend on their wintering grounds to supply the bulk of their diet," Laidre
says.
Global
Warming Threat
In 2008, Laidre and Heide-Jorgensen's research flashed briefly into public view
with the publication of an international consensus report that ranked narwhals as
edging out even polar bears as the Arctic mammal most vulnerable to
climate-induced habitat change. According to the report, this extreme
sensitivity to global warming stems directly from the whale's small range,
narrow migration routes, limited world population and restricted diet. Combine
these traits with the narwhal's low genetic diversity and, Heide-Jorgensen
says, "I think you can understand what makes them so vulnerable."
Just
how global warming will affect the narwhal's environment remains unclear.
Counterintuitively, one possibility is that warming will further reduce the
scant open water that ensures winter survival for narwhals. Such a cooling
trend could result from the increased rainfall that global warming can produce
in coastal regions. The increased influx of freshwater decreases ocean
salinity, which can slow or shut down ocean currents that would normally
deliver warmth from the Equator. In line with such predictions, in 2005 Laidre
and Heide-Jorgensen reported that Baffin Bay sea ice cover had been steadily
increasing since 1978. During this time, the percentage of open water at the
end of winter had shrunk to an average of just one half of 1 percent. "Now that
seems to have reversed," Laidre says of the last four years. "Instead we're now
seeing less and less ice cover."
Unfortunately,
increased open water could bring its own problems. One major concern is that
rising water temperatures could render the narwhal's ecosystem less
productive--particularly in regard to the cold-water turbot that provide the
whale its primary food source. Another is the possibility that fishing fleets
will begin entering the narwhal's previously ice-locked feeding areas. "Both
Canada and Greenland have looked at extending their coastal fisheries
offshore," Laidre says. "With reduced ice cover, that interest will only
continue." Indeed, the international competition for nearby fisheries has been
so fierce at times as to escalate into armed conflict. During the so-called
Turbot War of 1995, the Canadian Coast Guard used machine guns and water
cannons to disrupt and seize Spanish trawlers plundering Newfoundland's Grand
Banks. Whichever direction global warming takes Baffin Bay, environmental
shifts are already in motion. "The whole ecosystem is changing, not just with
respect to narwhals," Laidre says.
A
Promising Role
Baffin Bay's narwhals may play a pivotal role in better understanding these
changes. Over the past two years, Laidre and Heide-Jorgensen have used a grant
from the National Oceanic and Atmospheric Administration to harness 10 narwhals
with satellite transmitters. The transmissions relayed the animals' positions
and surrounding water temperatures as the whales made thousands of winter dives
to the bottom of Baffin Bay.
Laidre
tracked the narwhals' daily movements from her computer monitor at the
University of Washington's Polar Science Center. Now that the last of the
transmitters has fallen away and sunk, she is beginning the daunting task of
analyzing the temperature data with the help of the science center's
oceanographers.
Preliminary
analysis suggests that the whales are diving at fronts--areas with large and
rapid temperature changes that stem from warm, upwelling waters. "On its own,
these data aren't going to reveal anything about global warming," Laidre says.
"But they can serve as a baseline for future studies, and, when combined and
compared with historical data, they may show differences from the past."
Already
the data transmitted from the outfitted narwhals are rivaling the meager
information collected through far more expensive, manned expeditions that
require research vessels to venture into iceberg-strewn waters, winch
instruments into the deep on cables and then return months later with the hope
of retrieving them.
Meanwhile,
the narwhal's short-term prospects look good, with populations appearing stable
in the decade since the governments of both Greenland and Canada forged hunting
quotas with the region's native Inuit peoples. The Inuit harvest several
hundred narwhals each year, both for the male's valuable tusk and for the
nutritious meat and vitamin-rich skin that have long helped Arctic peoples
survive on a diet largely devoid of fruits and vegetables.
Today,
Arctic researchers can still watch thousands of migrating narwhals passing by
their coastal camps in a single day--sometimes spaced apart only by the 9-foot-long
tusks of the males. Heide-Jorgensen describes being awed by both the view from
coastal cliffs and the sounds he hears from his tent under a midnight sun. He
describes the noise of a narwhal surfacing to breathe as somehow both
prehistoric and resembling the brake release of a diesel truck. "A kind of
whistle that ends with an airy sigh," he says. "And that's when you forget how
cold it is. It's just you and these ancient creatures with a life so special
and isolated from anything else."
Jessica
Snyder Sachs is the author of Good Germs, Bad Germs: Health and Survival in
a Bacterial World (Farrar, Straus, and Giroux, 2007).
The
Tale of the Tusks
Though
technically considered "toothed" whales (as opposed to filter-feeding whales
that have mouths lined with baleen), adult narwhals have no functioning teeth
inside their mouths. The male's tusk, which grows as long as 9 feet, begins as
one of six pairs of teeth inside the mouth of a fetus. Four pairs of those
teeth disappear before birth, leaving two pairs. One of these develops into the
cuspids, or "fangs," and the others into vestigial teeth. In males the left
cuspid continues to grow outward in a counterclockwise spiral, emerging through
the upper jaw and lip to form a spearlike tusk. Typically the right cuspid
remains imbedded in the upper jaw, but about one in 100 males sports double
tusks. Similarly, about one in six females will bear a single, shortened tusk.
Cetacean
Senior Citizen
Although
they live in a dangerous winter environment where the vagaries of sea ice can
lead to sealed breathing holes and death from suffocation, narwhals, according
to a recent study by Mads Peter Heide-Jorgensen of Greenland's Institute of
Natural Resources and his colleagues, has determined that the animals
nevertheless are among the longest-lived mammals.
To
determine the age of narwhals, the researchers studied changes in eye chemistry
that occur predictably as the animals age, using specimens from 75 dead narwhals
collected in West Greenland in 1993 and 2004. The oldest of the whales, a
female, was between 105 and 125 years old. The oldest male was between 75 and
93 years old. However, the animals in the study came from a heavily hunted
population. "The maximum age in other narwhal populations with less disturbed
age structure might be considerably higher," the biologists concluded in a
paper published in the Journal of Mammalogy. "Maximum age also is likely
to increase when more specimens are examined."
Biologists
have estimated the life span for a number of whale species, and some of them,
too, are long-lived. The oldest recorded orca, or killer whale, and the oldest
blue whale were both 90; the oldest fin whale reached 100. The real Methuselah
in the cetacean world is the bowhead, another species of Arctic seas; the
oldest on record lived 211 years.
Two
of the most familiar whales did not win the whale life span sweepstakes. Sperm
whales, the species of titular interest in the novel Moby Dick, live
about 70 years and humpbacks about 48.
