Whales Ravaging Otter Population Off
Alaska's Coast
October 16, 1998|By Usha Lee McFarling, INQUIRER WASHINGTON BUREAU
Hungry killer whales in Alaska's
Aleutian Islands are selecting a startling
new menu item. Instead of eating big,
blubbery sea lions, some are gobbling
sea otters by the thousands.
For top-level carnivores like
killer whales to choose an entirely new
type of prey, and for them to turn
suddenly on neighboring animals with
which they have coexisted for millennia,
could signal that Alaska's ocean
environment may be dramatically out of
kilter.
The change is leading some to
call for better monitoring of the seas,
including a possible overhaul of how the
country manages its ocean preserves.
“We are looking at an ecosystem
in dramatic flux,” said James Estes, a
wildlife biologist with the U.S.
Geological Survey and the lead author of
a report describing the phenomenon in
yesterday's issue of the journal Science.
“It's just one more indication of major
change going on in the ocean.”
Normally, killer whales passing
through Alaskan waters feast on sea
lions and seals. But the numbers of those
animals have dwindled to near nothing
in recent decades, probably because the
ground fish they eat are in decline.
The reasons for the decline
remain hotly debated. Commercial
fishing is blamed in part, but the fish are
also thought to be on the decline because
ocean waters there have warmed since a
1970s shift in deep ocean currents.
Without the fish, there are no sea
lions and seals. And without the sea
lions and seals, the killer whales appear
to be desperate.
Sea otters, because they are small
and contain very little blubber, are a
mere snack for killer whales, said Paul
Dayton, a professor of marine ecology at
the University of California at San
Diego.
“I think they're very hungry to be
eating those things,” Dayton said.
Sea otters were once hunted to
near extinction for their pelts, the
thickest on the planet. But with laws
protecting them, the animals have been
on the rebound in many areas since
1970. In 1990, though, otter numbers in
the Aleutians began falling by 25 percent
a year, said Estes, who for decades has
studied the animals and their role in the
ecosystem.
The decline was a mystery. There
was no sign of disease or toxins or
reproductive failure among the otters.
And they were not starving because their
favorite food - sea urchins - were still
clustered across the ocean bottom.
In 1991, researchers reported the
first surprising observation of a killer
whale eating an otter. Since then,
evidence has mounted that killer whales
were to blame for the loss of about
45,000 otters from a 2,000-mile stretch
of the Aleutians since 1990.
Since no otter carcasses were
washing on shore, it is likely the bodies
were consumed. (Sea otter bodies do not
sink because of the air trapped in their
lungs and fur.) Meanwhile, a lagoon
inaccessible to whales remains full of the
frisky mammals. And nine more
sightings of whales eating otters were
reported after 1991.
“In one attack, a killer whale just
came up from below with its mouth open
and engulfed an otter,” said Brian
Hatfield, a U.S. Geological Survey
biologist who described nine attacks in a
report in this month's issue of Marine
Mammal Science.
Given the calories contained in
an otter, whales on an otter-only diet
would need to eat about five a day to
survive, Terry Williams, a biologist at
the University of California at Santa
Cruz, calculated. That number led Estes
to calculate that all the missing otters
could be attributed to four whales - the
size of a typical killer whale hunting
party.
Because sightings are few, and
because killer whales in the Aleutians
have not been studied well enough to be
identified as individuals, it is unknown
whether the otter slaughter is due to
many whales eating a few each or to a
few whales concentrating mainly on the
furry creatures, Hatfield said.
In areas where the otters are gone, the
sea urchins they normally eat are
booming in number. While sushi lovers
might applaud, the urchins are causing a
problem by mowing through the kelp
forests that provide food and protection
to a large number of coastal species.
Whale predation is not affecting
the sea otters of California, likely
because seals and sea lions are in
abundance in the southern Pacific. But
otters there are in trouble for other
reasons, said Andrew Johnson, who runs
the Monterey Bay Aquarium's sea otter
research and conservation program.
Various toxins, including boat
hull paint, agricultural chemicals, and
natural poisons produced by plankton,
have been found in sea otter carcasses. It
is thought, but not proven, that the
contamination might be lowering the
animals' resistance to disease, which
kills large numbers of California otters.
In addition, this year's El Nino storms
battered many baby otters and their
mothers to death.
In both otter populations, it
appears that human and natural effects
are taking a heavy toll. The only way to
understand and prevent such problems
would be to create truly natural ocean
preserves where fishing and oil drilling
are completely prohibited, said Dayton,
the UC-San Diego professor, who argues
that current preserves allow too much
human interference.
“There's so much going on right
now,” he said. “And we don't have any
concept of what's natural.”
Name: ______________________________________ Period: ______ Date: _________
Directions: Read the article “Whales ravaging otter population off Alaska’s coast”.
Then answer the following questions.
1. What do killer whales normally feed on?
2. Killer whales are defined as a top carnivore. What does that mean?
3. What are killer whales starting to eat?
4. Why do killer whales not normally eat these animals?
5. Draw a food web for a Aleutian Island. Make sure to show normal otter and whale
feeding patterns. Please label producers, herbivores, and top predators.
6. What effect has the new feeding habits of whales had on the ecosystem of the
ocean off of the Aleutian Islands?
7. How many sea otters may have been eaten by killer whales? How many whales
may be responsible for this loss? Why may this be a good sign? What could
happen if other whales started using this feeding strategy?
8. Why are whales not effecting the otter populations of California? What is
effecting their populations?