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- An increase in the number of gray whale
deaths could be the result of a diminishing food supply, according to an
Oregon Sea Grant researcher.
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- At least 65 whales are reported to have
washed up on Mexico's Baja Peninsula, where the animals migrate each winter
to bear their young. And that's not all. Additional whale corpses have
been discovered along California shores in March and April during the migration
of the whales north to their feeding grounds in the Bering Sea.
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- The apparent higher-than-normal mortality
rate has generated widespread speculation. Some researchers point to pollution
or changes in seawater caused by a huge salt-evaporation plant in Guerro
Negro. Others suspect that the animals were killed by cyanide in fluorescent
dye used by drug smugglers to mark the sea during airdrops of illegal narcotics.
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- But Oregon Sea Grant whale researcher
Bruce Mate said the answer might lie in changes to the undersea ecosystem
in the whales' summer feeding grounds off Alaska.
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- Mate, who is based at Oregon State University's
Hatfield Marine Science Center, says one possibility for the gray whale
mortalities might be that they are not getting enough to eat. The animals
spend the summer months in the Bering Sea, between Alaska and Siberia,
where they fatten up mostly on bottom-dwelling creatures called amphipods.
The whales then fast during their entire migration south without any additional
snacking until they reach Alaska again the following summer.
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- "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."
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- Researchers have noted huge changes in
the Bering Sea 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.
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- 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 a 12,000-mile migration
from Alaska to the Baja Peninsula -- the longest migration of any marine
mammal.
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- Mate reviewed information on the gray
whale fatalities during a recent meeting of the Mexican Society for Marine
Mammalogy. Figures indicate that the number of fatalities is the highest
recorded in the 24 years that people have kept track of gray whale migrations.
The numbers may partly reflect the fact that, this year, people are keeping
better track of the whales, said Mate.
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- Most worthy of attention this year, is
the number of adult whales found dead, Mate said. According to his study,
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.
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- "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, more than 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."
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- Mate also notes that this year's fatalities
were spread out over a long stretch of coastline during a four-month period,
indicating to him that the deaths were not the result of a localized problem
such as pollution or drug-runners' dye.
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- But he admits it's hard to tell just
what is going on, particularly on the hot, isolated shores of Baja.
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- "Most whales are too far gone by
the time they come to shore. 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 said sometimes researchers are still able to
collect blubber specimens, "but even that literally melts away in
the heat."
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- Even those whales that wash up in the
more temperate shores of California can pose a challenge for researchers
because they have often been at sea for several days.
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- Mate hopes to expand his study next summer
if he can muster the required funding. He plans to tag the whales during
their northbound migration and to examine their activity in the Bering
Sea.
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- "If [the whales] stay in one spot,
it will indicate that they have found significant quantities of food,"
Mate explains. "Or if they move around a great deal it will suggest
that they haven't found what they are looking for either in quantity or
quality." Mate also intends to sample the actual food supply.
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- Anyone interested in adopting a gray
whale to aid Mate's study can write to the Hatfield Range Science Center,
Newport, Ore. 97365.
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