Density estimates of odontocetes in an active military base using passive acoustic monitoring

We deployed passive acoustic monitoring devices in Camp Lejeune, North Carolina, USA, to estimate density of odontocete populations. Four C-PODs (echolocation click detectors) were deployed in water depths ranging from 13 to 21 meters from 30 November 2012 to 13 November 2013. Two species of odontocetes are known to inhabit the survey area: bottlenose dolphins and Atlantic spotted dolphins. These methods incorporate (i) the rate at which the animals produce echolocation cues, (ii) the probability of detecting cues, and (iii) the false positive rate of detections. To determine the cue rate of bottlenose dolphins, we attached DTAGs to 14 bottlenose dolphins during 2012 and 2013 in Sarasota, Florida. To determine cue rate of spotted dolphins, we used six recordings of focal follows from 2001-2003 in an area adjacent to C-POD deployment locations. Echolocation playbacks to C-PODs were used to obtain false positive rate and detection radius of each C-POD. Furthermore, we obtained proportions of bottlenose and spotted dolphins in the survey area from concurrent line transect surveys. Preliminary results indicate that dolphins were detected on all four C-PODs during every month of the survey period. Future studies in areas where multiple species are present could potentially use methods described here.