Sound Findings; January 2005; Scientific American Magazine; by David Kosub; 2 Page(s)

The debate is as fierce and perennial as the surf pounding the Alaska coastline. On one side, commercial and sports fishermen complain that calculated fishing quotas do not match the number of fish actually in the water. On the other, conservation authorities worry that overfishing will deplete the sockeye and chinook salmon stocks plying the Pacific Northwest waters. New techniques using existing acoustic sonar equipment may help both sides by determining how many salmon are in the water as well as distinguishing one species from the other. And that could make counting and catching them a lot easier.

In sonar setups such as fish finders, pulses of sound bounce off the water's bottom--and off any creatures that happen to swim by. Typically devices record the strength of the return echo, thereby indicating the rough numbers of fish and their sizes.