A digital acoustic recording tag for measuring the response of marine mammals to sound

Abstract

There is growing concern about the effect on marine mammals of underwater sound sources such as vessels, industrial equipment, and sonar. In order to quantify the reaction of these animals to sound, controlled exposure experiments have been attempted using surface observations or vocal monitoring to estimate response. However, the short surface time of most marine mammals, and their often unknown vocalization rates, limit the effectiveness of such experiments. To address these problems, a small digital recording tag, the DTAG, has been developed capable of simultaneously sampling the acoustic environment of the host animal, together with its orientation, heading, and depth. The tag has a 400-Mbyte memory array sufficient to record audio and sensor signals for several hours. The tag is encapsulated in a plastic resin and can operate at a water depth up to 3000 m. Programing and data off-load are accomplished with an infrared communications link to a personal computer. The DTAG has been deployed on northern right whales and sperm whales using suction cup attachments. Delivery was by means of a cantilevered pole from a small boat. The resulting data indicate a number of behavioral response metrics as well as new results on dive behavior and vocalization rates.