What's Killing the Otters?. . .
A Whale of a Tale
Otters. The site of these joyful little creatures drifting on the ocean currents as they crack open shellfish snacks has turned the otter into a poster child of ecology. Eveyone loves them. Unfortunately, scientists suspect that killer whales may love them, too.
Scientists have documented a huge crash in the population of sea otters off Alaska's Aleutian Islands. Since 1990, the otter population has declined by 90%. Research conducted by the US Fish and Wildlife Service indicates that this decline has been repeated throughout the otters' range.
For some time, no one could figure out what was causing the rapid decline of the otter population. Disease and starvation were ruled out, because the rate of finding dead otters floating up on shore had not changed. Reduced fertility was ruled out, because there had been no change in the birth and survival rates of otter pups. Radio tagging showed that otters weren't simply moving from one area to another. That left an increase in the otter's mortality rate. In simpler words, something was killing them.
Then in 1991, researchers saw a killer whale gobble an otter. They were shocked. Sea otters and Orcinus orca (the killer whales) had co-existed peacefully for eons. Most people thought that whales just ate harbor seals and sea lions. But then nine more reports of killer whales eating otters came in.
There was one place, Clam Lagoon, that was home to sea otters, but inaccessible to whales. After careful testing of otter populations there, scientists had their answer. With no killer whales around, otter population were just what they had always been. There was no decline.
Scientists are concerned not just for the otter. By feeding on shellfish and sea urchins, otters help to maintain the underwater forests of kelp that provide food and refuge for a host of marine creatures. Scientists worry that the declining otter population means that the kelp beds will suffer.
Researchers are also concerned for the killer whales. They fear that the whales' change in diet from seal to otter is a symptom... that the real problem is the collapse of the area's food web brought about, perhaps, by overfishing.They think that the orca population must be pretty hungry to eat otters. For the whales, it must be like trying to survive on popcorn.
In the News
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