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No. 1403:
Vanishing Sea Otters

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)

Stevens, W,K., Search for Missing Otters Turns Up a Few Surprises. The New York TimesScience Times, Tuesday, January 5, 1999, pp. D1-D2.


The images of otters in this 1857 book on zoology generally
show the animal's purpose as being the object of hunters