Today, let's take a quick trip through a long food chain.
The University of Houston's College of Engineering
presents this series about the machines that make our
civilization run, and the people whose ingenuity created
them.
Sea otters are vanishing from
Alaska's waters. Sea otters are intelligent and playful
beasts. They're regarded as animal tool users because one
will lie back, place a rock on its chest, then crack open
clams and mussels by whacking them against the stone.
The New York Science Times now tells a disturbing
detective story about the sea otter decline. They were
nearly wiped out by 19th-century fur traders, but since
then their numbers have steadily risen. All animal
populations fluctuate, so marine ecologists with the US
Geological Survey weren't alarmed when the otter
population fell off in 1990.
But the drop soon proved to be far more than statistical
noise. By 1993 Alaska's otter population was down by
half, and today it's only a tenth of what it was
before 1990. Why?
In 1991, observers saw something quite unexpected. An
Orca, a killer whale, was seen eating an
otter. Orcas and otters were supposed to coexist. More
such sightings confirmed the terrible truth. But why had
whales suddenly turned on otters?
Then the ecologists found that the population of
nutritious ocean perch and herring were also declining.
Orcas don't eat those fish, but seals and sea lions
do. And seals and sea lions are what'd formerly
been supper for Orcas. Sure enough, the seal and sea lion
population had also declined.
So otters have vanished because the fish, which they
never ate in the first place, have vanished. Now the
ripple spreads: otters are no longer there to eat sea
urchins on the ocean floor, so the sea urchin population
has exploded. But sea urchins live off kelp forests
growing from the sea bottom, so they're killing off the
kelp. Kelp in turn has been home to fish that feed
seagulls and eagles. Like Orcas, seagulls can find other
food, but bald eagles can't, and they're in
trouble.
Now this seems to've begun with the decline of ocean
perch and herring, so why are they dying? Well, Japanese
whalers have been killing off the variety of whales that
eat the same microscopic organisms that feed
pollock. With more to eat, pollock flourish. They
in turn attack the perch and herring that were food for
seals and sea lions. So all this chaos comes down to the
slaughter of whales.
This is so hideously complicated that it looks like
low-brow comedy. However, an ecological rule of thumb
says that the larger the species you exterminate, the
more widespread the effect will
be. In this case, sea otters are only one of many
casualties of whaling. We notice some dying species, like
the adorable sea otter. Others, like kelp forests, are
out of our line of sight.
It isn't often that one agency is able to muster enough
data to provide this kind of global view. This is a rare
glimpse of the big picture. Now that we have it, what we
see is neither pretty nor comforting.
I'm John Lienhard, at the University of Houston, where
we're interested in the way inventive minds work.
(Theme music)
