(…) In the present study, we investigated whether this documented conflict between bottlenose dolphins and harbor porpoises in California affected harbor porpoise behavior within the nearshore environment where habitat overlap occurs with bottlenose dolphins. We expected to find lower densities of harbor porpoises when bottlenose dolphins were present than when they were absent.
We used data from moored click detectors (C-PODs; Chelonia Ltd., http://www.chelonia.co.uk) which were deployed at a study site in Monterey Bay (Fig. 1) to quantify the relative presence of harbor porpoises as well as bottlenose dolphins. These data were collected as part of a separate study but provided an opportunity to examine the acoustic behavior of both species within a few kilometers of the sites where bottlenose dolphin attacks on harbor porpoises were observed by Cotter et al. (2012) in previous years. (…)