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 nusually high numbers of dead gray whales have been
washing up on the shores of Mexico and the western U.S. this
year, causing speculation that something, somewhere, may be killing
off the giant marine mammals. But Oregon Sea Grant whale expert
Dr. Bruce Mate believes the answer may lie in changes to the
undersea ecosystem in the whales' summer feeding grounds off
Alaska.
 At least
65 gray whales were found dead this winter along the coast of
Mexico's Baja Peninsula, where the animals migrate each winter
to bear their young. Still more washed up along California shores
in March, April and May as the whales migrated north to the Bering
Sea.
The apparently
higher-than-normal mortality rate has given rise to plenty of
speculation. Some blame the deaths on pollution or sea-water
changes caused by a huge salt-evaporation plant in Baja. Others
suspect that the animals were killed by cyanide in a fluorescent
dye used by drug smugglers to mark the sea during air drops of
illegal narcotics.
Mate, a marine
biologist and marine mammal specialist for Oregon Sea Grant at
Oregon State University, says neither suggestion is likely. A
more likely cause could be massive changes to undersea animal
communities in the Bering Sea where the whales spend their summers
feeding and rearing their young. Mate, who is based at OSU's
Hatfield Marine Science Center, reviewed information on the gray
whale fatalities during a recent meeting of the Mexican Society
for Marine Mammalogy.
Figures show
that the number of fatalities is the highest recorded in the
24 years that people have kept track of gray whale migrations.
But Mate says the numbers may partly reflect the fact that, this
year, people worked harder to count the whales. Just as many
could have died in earlier years, he said, but gone unnoticed.
What was notable
this year, according to Mate, is the number of adult whales found
dead. He says more than half of the 65 dead gray whales counted
in Mexico were adults, and quite a few of the rest were at least
one year old. That's a marked contrast to most years, when observable
gray whale corpses are typically very young a few weeks or a
few months old.
"Typically,
most of the animals you'd expect to see die during the reproductive
season would be newborn calves," Mate said. "Only about
50 percent of calves live to one year of age. But this year,
over half of the dead animals are adults and quite a significant
number of the rest are yearlings. This is part of the population
we're not used to identifying with such high mortality rates."
Despite widespread
speculation about the whale deaths, Mate noted that this year's
fatalities were spread out over a long stretch of coastline during
a four-month period, so Mate and his colleagues do not think
it was the result of a localized problem such as pollution or
drug-runners' dye. But he admits it's hard to tell just what
is going on, particularly on the hot, rugged shores of Baja.
"It's
been virtually impossible to get good diagnostic information
on the cause of death for these animals because the area is so
remote," Mate said. "By the time a team can identify
a mortality and get to it, the warmth of the sun has caused bloating
and deterioration in the physiology of the carcass, so good diagnostics
really can't be done."
Mate says
one possibility for the gray whale mortalities might be that
they are not getting enough to eat during the summer. The animals
spend the summer months in the Bering Sea between Alaska and
Siberia. They fatten up there and then fast during the migration
south, and they don't eat during the winter or in the spring
when they head north again.
"So gray
whales might go without food anywhere from three to five months,"
Mate said, "and those that didn't fill up the tank, so to
speak, in the Bering Sea may be returning on empty."
Gray whales
feed on bottom-dwelling creatures in the Bering Sea. Researchers
have noted huge changes there at all levels of the food chain,
and some have theorized that those changes are part of an even
larger disruption of ocean temperature and biomass patterns.
Mate says
those changes might be affecting the amount of food the gray
whales can find during the summer and they need a lot of food.
Not only do they need to fatten up to get through the months
when they don't eat, they also need fuel for the survive a 12,000-mile
migration from Alaska to the Baja Peninsula the longest migration
of any marine mammal. 
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hmsc.orst.edu or Ben Sherman, Sea Grant National Media Relations, 202-662-7095, sherman@nasw.org