Abstract: This invention provides a device and method for measurement of the actual on-bottom time of a sampling otter trawl used for benthic sampling. The device uses passive measurement of the actual on-bottom time without cables and wires connected to the ship, and is small enough to be mounted on a standard otter trawl door without affecting its net-towing function. The apparatus consists of a sealed bottom contacting and counting sensor which totalizes and displays the accumulated on-bottom time. Power is supplied from a self-contained battery which may be automatically recharged by a solar cell. In operation, a flexible trigger arm is mounted so as to extend below the runner on the bottom edge of the trawl door. When bottom contact is first made, the trigger arm bends and mechanically causes a magnet to move sufficiently close to actuate a magnetic switch inside a transparent electronic data module. An electronic counter inside the module will count minutes and seconds as long as the magnetic switch is closed.