RESUMEN
The continuing rise in underwater sound levels in the oceans leads to disturbance of marine life. It is thought that one of the main impacts of sound exposure is the alteration of foraging behaviour of marine species, for example by deterring animals from a prey location, or by distracting them while they are trying to catch prey. So far, only limited knowledge is available on both mechanisms in the same species. The harbour porpoise (Phocoena phocoena) is a relatively small marine mammal that could quickly suffer fitness consequences from a reduction of foraging success. To investigate effects of anthropogenic sound on their foraging efficiency, we tested whether experimentally elevated sound levels would deter two captive harbour porpoises from a noisy pool into a quiet pool (Experiment 1) and reduce their prey-search performance, measured as prey-search time in the noisy pool (Experiment 2). Furthermore, we tested the influence of the temporal structure and amplitude of the sound on the avoidance response of both animals. Both individuals avoided the pool with elevated sound levels, but they did not show a change in search time for prey when trying to find a fish hidden in one of three cages. The combination of temporal structure and SPL caused variable patterns. When the sound was intermittent, increased SPL caused increased avoidance times. When the sound was continuous, avoidance was equal for all SPLs above a threshold of 100 dB re 1 µPa. Hence, we found no evidence for an effect of sound exposure on search efficiency, but sounds of different temporal patterns did cause spatial avoidance with distinct dose-response patterns.
Asunto(s)
Exposición a Riesgos Ambientales/análisis , Ruido , Phocoena/fisiología , Animales , SonidoRESUMEN
Safety criteria for naval sonar sounds are needed to protect harbor porpoise hearing. Two porpoises were exposed to sequences of AN/SQS-53C sonar playback sounds (3.5-4.1 kHz, without significant harmonics), at a mean received sound pressure level of 142 dB re 1 µPa, with a duty cycle of 96% (almost continuous). Behavioral hearing thresholds at 4 and 5.7 kHz were determined before and after exposure to the fatiguing sound, in order to quantify temporary threshold shifts (TTSs) and hearing recovery. Control sessions were also conducted. Significant mean initial TTS1-4 of 5.2 dB at 4 kHz and 3.1 dB at 5.7 kHz occurred after 30 min exposures (mean received cumulative sound exposure level, SELcum: 175 dB re 1 µPa2s). Hearing thresholds returned to pre-exposure levels within 12 min. Significant mean initial TTS1-4 of 5.5 dB at 4 kHz occurred after 60 min exposures (SELcum: 178 dB re 1 µPa2s). Hearing recovered within 60 min. The SELcum for AN/SQS-53C sonar sounds required to induce 6 dB of TTS 4 min after exposure (the definition of TTS onset) is expected to be between 175 and 180 dB re 1 µPa2s.
Asunto(s)
Fatiga Auditiva , Exposición a Riesgos Ambientales/efectos adversos , Audición , Ruido/efectos adversos , Phocoena/fisiología , Estimulación Acústica , Animales , Femenino , Pruebas Auditivas , Masculino , Phocoena/psicología , Recuperación de la Función , Medición de Riesgo , Factores de TiempoRESUMEN
In seismic surveys, reflected sounds from airguns are used under water to detect gas and oil below the sea floor. The airguns produce broadband high-amplitude impulsive sounds, which may cause temporary or permanent threshold shifts (TTS or PTS) in cetaceans. The magnitude of the threshold shifts and the hearing frequencies at which they occur depend on factors such as the received cumulative sound exposure level (SELcum), the number of exposures, and the frequency content of the sounds. To quantify TTS caused by airgun exposure and the subsequent hearing recovery, the hearing of a harbor porpoise was tested by means of a psychophysical technique. TTS was observed after exposure to 10 and 20 consecutive shots fired from two airguns simultaneously (SELcum: 188 and 191 dB re 1 µPa2s) with mean shot intervals of around 17 s. Although most of the airgun sounds' energy was below 1 kHz, statistically significant initial TTS1-4 (1-4 min after sound exposure stopped) of â¼4.4 dB occurred only at the hearing frequency 4 kHz, and not at lower hearing frequencies tested (0.5, 1, and 2 kHz). Recovery occurred within 12 min post-exposure. The study indicates that frequency-weighted SELcum is a good predictor for the low levels of TTS observed.
Asunto(s)
Fatiga Auditiva , Conducta Animal , Exposición a Riesgos Ambientales/efectos adversos , Ruido/efectos adversos , Phocoena/psicología , Estimulación Acústica , Acústica , Animales , Audición , Masculino , Phocoena/fisiología , Psicoacústica , Recuperación de la Función , Medición de Riesgo , Espectrografía del Sonido , Factores de TiempoRESUMEN
To study intra-species variability in audiograms, the hearing sensitivity of a six-year-old female and a three-year-old male harbor porpoise was measured by using a standard psycho-acoustic technique under low ambient noise conditions. The porpoises' hearing thresholds for 13 narrow-band sweeps with center frequencies between 0.125 and 150 kHz were established. The resulting audiograms were U-shaped and similar. The main difference (25 dB) in mean thresholds between the two porpoises was at the high-frequency end of the hearing range (at 150 kHz). Maximum sensitivity (47 dB re 1 µPa for the female and 44 dB re 1 µPa for the male) occurred at 125 kHz. The range of most sensitive hearing (defined as within 10 dB of maximum sensitivity) was from 16 to â¼140 kHz. Sensitivity declined sharply above 125 kHz. All five porpoises for which a valid behavioral audiogram now exists were rehabilitated stranded animals, all were tested with similar psycho-acoustic techniques, and all had similar audiograms. The present study provides further evidence to confirm that the hearing range and sensitivity of the first three harbor porpoises, which have been used in secondary research and on which policy decisions have been based, are representative of those of young harbor porpoises in general.