Abstract:

Harbor porpoises are incidentally taken in various sink gillnet fisheries nationally. Little is known about the mechanism of these entanglements. To protect these animals as required by the Marine Mammal Protection Act (MMPA), fishery managers use time area closures and/or permit the use of acoustic deterrent devices (pingers) to reduce bycatch. To understand how an entanglement occurs and how the pingers function, one must understand the underwater behavior of the animals. Studies of captive porpoises, and using mounted instrumentation on released animals, have shown some aspects of porpoise life history but may or may not reveal natural behavior. A research program was initiated to determine the feasibility of passively tracking wild harbor porpoise using their echolocation signals (clicks) and observing their underwater movements in three dimensions. Additionally, details of these movements during feeding, traveling, and social events may provide an insight into their behavior that makes them prone to entanglement. Preliminary results demonstrate that the underwater tracking of harbor porpoises can be accomplished using this technique and several aspects of the animal's natural behavior and communication are presented. A next generation autonomous system, to be deployed near actively fishing sink gillnets being developed, is described. [Work supported by NMFS and the URI/NOAA CMER Program.]