USING PASSIVE ACOUSTICS TO MONITOR BOTTLENOSE DOLPHIN (TURSIOPS TRUNCATUS) USE OF TWO MILITARY RANGES IN PAMLICO SOUND, NORTH CAROLINA

Abstract

A passive acoustic monitoring device to detect bottlenose dolphin (Tursiops truncatus) presence in two military ranges in Pamlico Sound, NC is being developed by researchers at the Duke University Marine Lab. Potential adverse effects of military activities in these ranges include temporary or permanent hearing loss, tissue damage, altered habitat use, and changes in behavior. The real-time passive acoustic monitoring system allows for automated detection of bottlenose dolphin whistles and alerts the Marine Core Air Station (MCAS) Cherry Point when dolphin whistles are detected. Passive acoustic monitoring relies on the detection of vocalizations, so I conducted focal follows coupled with acoustic monitoring to determine group vocalization rates. Dolphins near the ranges produced at least one detectable whistle in 25% of one-minute bins. Behavioral state and group size affected whistle production, and probability of whistle presence was significantly higher for socializing dolphins and groups of 1-2 and 11-20 dolphins. I examined focal follow tracks to determine rates of travel and calculated potential residence time for dolphins in the range. The average rate of travel for dolphins in the area was 0.871m/s, and rate of travel when traveling was significantly higher than any other behavior state. Residence time was also influenced by behavioral state and group size. The probability of whistle production is sufficient for an automated real-time passive acoustic detection device to detect bottlenose dolphins. Results of this study could be used by MCAS Cherry Point to establish procedures that will mitigate harmful effects to bottlenose dolphins without sacrificing military readiness. This type of system has potential for use at other coastal military ranges, bridge demolitions and other near shore activities posing threats to coastal dolphin populations and other marine mammals.