IMIS

Traditional marine mammal monitoring techniques, such as visual surveys, are not feasible under certain conditions, such as poor weather, darkness, and conflicts with other human activities. In such cases, alternative monitoring tools are required. We used autonomous acoustic recorders, designed by Cornell University, to monitor bottlenose dolphin (Tursiops truncatus) use of two ranges in Pamlico Sound, North Carolina, in which the United States Marine Corps conducts military training exercises. We deployed multiple units in the shallow waters of both ranges for more than a year. The recorders were programmed to sample at 12 kHz with a 12 kHz anti-aliasing filter. They were set on a duty cycle and of every hour, they recorded for either 10 or 30 consecutive minutes (bins of time referred to as "observation periods"). We analyzed the acoustic recordings using Raven 1.2.1 (Cornell Lab of Ornithology). We noted the presence or absence of dolphin whistles and clicks in each observation period to determine daily and seasonal patterns of dolphin occurrence in the two ranges. Vocalizing dolphins occurred frequently in both ranges throughout the year, with peaks of activity in June in both ranges and peaks in October, November, and December in one range. Vocalizing dolphins were detected more frequently in the late night and early morning hours than in the middle of the day and early night. We believe that such autonomous acoustic monitoring systems hold great promise for the management and mitigation of potentially adverse human activities on marine mammals. Observation dates and times are in GMT. Observations represent presence of whistles during a given duration observation period, either 10 or 30 minutes. Number of observations is the number of observation periods with whistles present. Number of animals is unknown and should not be inferred: a single individual may be represented by multiple observations and likewise a single observation period may include recordings from multiple individuals.