Crab traps and terrapins.

Build a better crab trap and they will come--but turtles will get away.

That was the aim, and the outcome, of a study by Willem M. Roosenburg of Ohio University in Athens and his colleagues. They modified a standard crab trap to prevent aquatic turtles, or terrapins, from drowning when they are accidentally caught in one. In terms of crab yield, the new traps worked just as well as the standard version, the researchers report in the October Conservation Biology.

Diamondback terrapins frequent some of the same shallow waters along the Atlantic coast as crabs do, and they are attracted by the same fish or other bait used in crabbing. Large numbers of terrapins can end up dead in the process--on average, one terrapin per day per five crab traps. Roosenburg says he once found 49 drowned in a single trap.

It's a major problem facing terrapins, which are considered threatened along much of the East Coast, says Roosenburg, who studies the animal's evolutionary ecology. "People are noticing tremendous declines in areas where commercial crabbing can go on in shallow waters," he says. The researchers report that 15 to 78 percent of a local population may be captured per year.

The modified crab trap stands above the water, allowing terrapins to breathe if they are caught. The trap may work well for recreational crabbing in shallow waters, but it is too cumbersome to fit on commercial boats. This drawback inspired researchers to come up with another device. A wire panel designed to fit onto the standard pots reduces the number of trapped terrapins by 75 percent, says Roosenburg, without affecting the number or size of crabs caught.