Will harbor porpoises (Phocoena phocoena) be deterred by a pinger that cannot be used as a “dinner bell” by seals?

Abstract

AbstractA measure proven successful in mitigating harbor porpoise bycatch, is the use of acoustic deterrents, i.e., pingers. However, most pingers are audible to seals. This may lead to seals associating pinger sounds with easily accessible food, leading to increased depredation, damage, and bycatch. In this study we tested if an experimental pinger, emitting sounds over 30 hr ON/OFF cycles, with low frequency components potentially audible to seals only at close distances, would effectively deter harbor porpoises. The porpoise response was measured by logging echolocation clicks, using C‐POD click detectors, moored at different distances from the pinger. In addition, we calculated the theoretical pinger detection range for seals. Results showed that the pinger had a significant negative effect on the porpoise click activity logged at 0 m and 100 m distance but not at 400 m from the pinger. During pinger ON periods, we found no significant increase in echolocation over consecutive days of the study, suggesting no habituation to pinger sounds. Our theoretical detection distances indicate that seals can only detect the pinger at close distances, preventing seals from using this pinger as a “dinner bell.”