<p>An understanding of sensory ecology, how animals receive and respond to their environment, can be a powerful tool for the conservation of endangered species because it can allow us to assess the potential success of actions designed to mitigate particular threats. We have a general understanding of how sea turtles perceive and respond to certain visual, magnetic, and chemical cues, but we understand very little about how they perceive and respond to acoustic cues. This dissertation explores the acoustic ecology of sea turtles, focusing on their auditory capabilities, responses to acoustic stimuli and the implications of this knowledge for their conservation. I measured the underwater and aerial hearing sensitivities of juvenile green (Chelonia mydas), hatchling leatherback (Dermochelys coriacea), and hatchling hawksbill (Eretmochelys imbricata) sea turtles by recording auditory evoked potential responses to tonal stimuli. Green turtles detected tonal stimuli between 50 and 1,600 Hz underwater (maximum sensitivity: 200-400 Hz) and 50 and 800 Hz in air (maximum sensitivity: 300-400 Hz), leatherbacks detected tonal stimuli between 50 and 1,200 Hz underwater (maximum sensitivity: 100-400 Hz) and 50 and 1,600 Hz in air (maximum sensitivity: 50-400Hz), and hawksbills detected tonal stimuli between 50 and 1,600 Hz in both media (maximum sensitivity: 200-400 Hz). Sea turtles were more sensitive to aerial than underwater stimuli when audiograms were compared in terms of sound pressure, but they were more sensitive to underwater stimuli when audiograms were compared in terms of sound intensity. I also examined the behavioral responses of loggerhead sea turtle (Caretta caretta) to simulated low frequency acoustic deterrent devices (ADDs) and found that these turtles exhibited a mild, aversive response to these sounds. This finding indicates that low frequency tonal ADDs have the potential to warn sea turtles of the presence of fishing gear and suggest that field tests of ADDs are warranted. Finally, I conducted a comprehensive review of our knowledge of the acoustic ecology of sea turtles, examined the sources of marine anthropogenic sound sea turtles are able to detect, evaluated the potential physiological and behavioral effects of anthropogenic sound, identified data gaps, and made recommendations for future research.</p> / Dissertation

Incidental bycatch in gillnets is a substantial threat to small cetaceans. Using Acoustic Deterrent Devices, “pingers”, have successfully reduced bycatch of harbour porpoises in gillnets. However, seals can use pingers as “dinner-bells” to easier find gillnets in order to raid and destroy them, further aggravating the existing conflicts between seals and coastal fisheries. Therefore, in the present study, the efficiency of two alleged “seal-safe” pingers, an experimental Banana pinger “SSB” and a Future Oceans F70 pinger “FO”, in deterring harbour porpoises from the vicinity of gillnets and thereby reducing bycatch in commercial gillnet fisheries, was tested. This was done by deploying click detectors, “C-PODs”, recording Detection Positive Minutes per hour, at each end of gillnets, provided with the two pinger types or no pingers at all. Bycatch instances were recorded into logbooks by participating fishermen and verified using video footage from on-board video cameras. Results showed that video monitoring was a reliable method for verifying the number of bycatches of porpoises and seals, but not seabirds, recorded in the fishermen’s logbooks. The experimental SSB pingers and the FO pingers significantly reduced porpoise presence, measured as Detection Positive Minutes per hour in the vicinity of the nets, compared to gillnets without pingers. However, the sample size was too small to yield a significant result regarding the bycatch reducing efficiency and dinner bell effect of the experimental pingers. Nevertheless, bycatch trends suggest that pingers did in fact reduce porpoise bycatch. Although both successful, FO pingers were slightly more efficient in deterring porpoises than SSB pingers. The SSB pinger sounds had bigger directionality variations than the FO pinger, which may have affected its deterrent effects. Therefore, additional trials are needed to further investigate this aspect.