BOURNE, Mass. -- Fishery managers trying to protect rare sea turtles from dying in fishing nets have tapped a Cape Cod company to build a device they think can help balance turtle protection with profitable fishing.

The "tow-time logger" is a 7-inch, silver cylinder that attaches to fishing nets and records how long the net stays underwater.

That time is crucial if a turtle gets snared in the nets dragged behind fishing trawlers. Federal research indicates the vast majority of sea turtles survive entanglement -- but only if the net is pulled up in less than 50 minutes.

With the logger, regulators can avoid other, potentially more onerous, restrictions on perpetually struggling fishermen -- such as shutting down fishing areas or requiring turtle-saving gear that doesn't work well in all nets. In fisheries where they decide time limits would work best, they wouldn't have to depend on an honor system to make sure nets are pulled up in time.

The logger was built under a $25,000 federal contract with the National Oceanic and Atmospheric Administration by Onset Computer Corp., a Bourne-based supplier of data loggers for energy and environmental monitoring. It starts recording water depth every 30 seconds once the net drops below two meters. If the net stays under beyond a preset time limit, the logger records it, and the infraction can be discovered when regulators download its data.

The device's early tests at sea have been successful, and work is ongoing to toughen it for the real-life rigors.