Frequency of greatest temporary hearing threshold shift in harbor seals (Phoca vitulina) depends on fatiguing sound level

Harbor seals may suffer hearing loss due to intense sounds. After exposure for 60 min to a continuous 6.5 kHz tone at sound pressure levels of 123-159 dB re 1 µPa, resulting in sound exposure levels (SELs) of 159-195 dB re 1 μPa2s, temporary threshold shifts (TTSs) in two harbor seals were quantified at the center frequency of the fatiguing sound (6.5 kHz) and at 0.5 and 1.0 octaves above that frequency (9.2 and 13.0 kHz) by means of a psychoacoustic technique. Taking into account the different timing of post-exposure hearing tests, susceptibility to TTS was similar in both animals. The higher the SEL, the higher the TTS induced at frequencies above the fatiguing sound's center frequency. Below ∼179 dB re 1 μPa2s, the maximum TTS was at the center frequency (6.5 kHz); above ∼179 dB re 1 μPa2s, the maximum TTS was at half an octave above the center frequency (9.2 kHz). These results should be considered when interpreting previous TTS studies, and when estimating ecological impacts of anthropogenic sound on the hearing and ecology of harbor seals. Based on the results of the present study and previous studies, harbor seal hearing, in the frequency range 2.5-6.5 kHz, appears to be approximately equally susceptible to TTS.status: publishe

High Levels of Food Intake in Harbor Porpoises (Phocoena phocoena): Insight into Recovery from Disturbance

If harbor porpoises (Phocoena phocoena) are impaired in their foraging ability because they need to move away from anthropogenic sound sources, their fitness may be reduced. Understanding how much harbor porpoises can eat after a disturbance, and how quickly they can replenish their energy reserves, is important for assessing the significance of disturbances. After fasting for various time periods (2 to 24 h), four captive harbor porpoises, housed in water and air temperatures similar to those encountered by wild conspecifics, were fed a structured diet of meals larger than usual (each normal meal was 20% of the daily food mass requirement). A few times they were fed ad libitum, but this led to severe constipation, so this feeding method was abandoned for welfare and health reasons. The food ingested over a period of one hour following fasting for 2 to 24 hours was quantified (i.e., mass, volume, and as a percentage of normal daily food mass intake in that period). The results show that, in contrast to established belief, harbor porpoises can eat a large percentage (up to ~98%) of their normal daily food mass intake in a single feeding bout without showing physical problems. Adult animals of around 155 cm in body length can eat up to ~3 kg (~2,700 ml) in one feed. If food is abundantly available after a period of fasting due to a disturbance, wild harbor porpoises could eat a large percentage of their daily energetic requirement in one feeding bout to compensate for the period of fasting. However, if food availability is limited in terms of prey numbers, size, or species, or if the fish are widely dispersed (so that more time is required to find and capture them), this may limit or reduce the speed of the recovery of body mass and blubber layer

Acoustic dose-behavioral response relationship in sea bass (Dicentrarchus labrax) exposed to playbacks of pile driving sounds

The foundations of offshore wind turbines are attached to the sea bed by percussion pile driving. Pile driving sounds may affect the behavior of fish. Acoustic dose-behavioral response relationships were determined for sea bass in a pool exposed for 20 min to pile driving sounds at seven mean received root-mean-square sound pressure levels [SPLrms; range: 130-166 dB re 1 μPa; single strike sound exposure level (SELss) range: 122-158; 6 dB steps]. Initial responses (sudden, short-lived changes in swimming speed and direction) and sustained responses (changes in school cohesion, swimming depth, and speed) were quantified. The 50% initial response threshold occurred at an SELss of 131 dB re 1 μPa2 s for 31 cm fish and 141 dB re 1 μPa2 s for 44 cm fish; the small fish thus reacted to lower SELss than the large fish. Analysis showed that there is no evidence, even at the highest sound level, for any consistent sustained response to sound exposure by the study animals. If wild sea bass are exposed to pile driving sounds at the levels used in the present study, there are unlikely to be any adverse effects on their ecology, because the initial responses after the onset of the piling sound observed in this study were short-lived.</p

Temporary Hearing Threshold Shift in Harbor Porpoises (Phocoena phocoena) Due to One-Sixth-Octave Noise Band at 32 kHz

Temporary hearing threshold shift (TTS) caused by fatiguing sounds in the 1.5 to 16 kHz range has been documented in harbor porpoises (Phocoena phocoena). To assess impacts of anthropogenic noise on porpoise hearing, TTS needs to be investigated for other frequencies, as susceptibility appears to depend on the frequency of the fatiguing sound. TTS was quantified after two porpoises (Porpoises F05 and M06) were exposed for 1 hour to a continuous one-sixth-octave noise band centered at 32 kHz, at average received sound pressure levels of 118 to 148 dB re 1 µPa, and at a sound exposure level (SEL) range of 154 to 184 dB re 1 µPa2s. Hearing thresholds for 32, 44.8, and 63 kHz tonal signals were determined before and after exposure to quantify initial TTS and recovery. Porpoise M06’s hearing was tested 1 to 4 min after exposure. At 32 kHz, the lowest SEL that resulted in significant TTS1-4 (3.4 dB) was 166 dB re 1 µPa2s. At 44.8 kHz, the lowest SEL that resulted in significant TTS1-4 (5.2 dB) was 178 dB re 1 µPa2s. The highest TTS1-4 (18.3 dB) occurred at 44.8 kHz after exposure to 184 dB SEL. Porpoise F05’s hearing was tested 12 to 16 min after exposure. At 32 kHz, the lowest SEL that resulted in significant TTS12-16 (3.5 dB) was 184 dB re 1 µPa2s. At 44.8 kHz, the lowest SEL that resulted in significant TTS12-16 (1.2 dB) was 178 dB re 1 µPa2s. The highest TTS12-16 (8.2 dB) occurred in Porpoise F05 at 44.8 kHz after exposure to 184 dB SEL. At 63 kHz, no TTS could be elicited in either animal. Considering that Porpoise F05 had more time than Porpoise M06 for recovery, the susceptibility of the two porpoises to TTS after exposure to sounds of 32 kHz was similar. In the range investigated so far (1.5 to 32 kHz), susceptibility to TTS appears to increase with increasing frequency below ~6.5 kHz, and to decrease with increasing frequency above ~6.5 kHz

Temporary hearing threshold shift in harbor seals (Phoca vitulina) due to a one-sixth-octave noise band centered at 16 kHz

Temporary hearing threshold shifts (TTSs) were investigated in two adult female harbor seals after exposure for 60 min to a continuous one-sixth-octave noise band centered at 16 kHz (the fatiguing sound) at sound pressure levels of 128-149 dB re 1 μPa, resulting in sound exposure levels (SELs) of 164-185 dB re 1 μPas. TTSs were quantified at the center frequency of the fatiguing sound (16 kHz) and at half an octave above that frequency (22.4 kHz) by means of a psychoacoustic hearing test method. Susceptibility to TTS was similar in both animals when measured 8-12 and 12-16 min after cessation of the fatiguing sound. TTS increased with increasing SEL at both frequencies, but above an SEL of 174 dB re 1 μPas, TTS was greater at 22.4 kHz than at 16 kHz for the same SELs. Recovery was rapid: the greatest TTS, measured at 22.4 kHz 1-4 min after cessation of the sound, was 17 dB, but dropped to 3 dB in 1 h, and hearing recovered fully within 2 h. The affected hearing frequency should be considered when estimating ecological impacts of anthropogenic sound on seals. Between 2.5 and 16 kHz the species appears equally susceptible to TTS