A little information on Cetaceans and underwater noise courtesy of Marine Scotland, with some top tips for the Port Authority on conducting a noise assessment:
Many forms of marine life, particularly cetaceans, use sound as their primary sense, for navigation, finding food and communication. Therefore they could be affected by the noise and vibration resulting from a range of marine activities. Cetacean species can be classified into three functional hearing groups based on auditory sensitivity:
Low Frequency (7 Hz – 22 kHz), all baleen whales e.g. humpback whales, minke whales Medium Frequency (150 Hz – 160 kHz), e.g. dolphins and killer whales
High Frequency (200 Hz – 180 kHz), e.g. harbour porpoises
Certain sounds such as drilling, explosive use, pile driving, sonar and acoustic deterrent devices may therefore not be heard by all cetacean species, or at least not heard with the same loudness. The degree of sensitivity contributes to the potential of a disturbance or injury offence. Auditory injury is deemed to have occurred when there is a permanent shift in the hearing threshold of cetaceans. Note that auditory injury can result from very loud noises, even if they are not within the frequency range of the animal (i.e. they can’t be heard by the animal but may still damage the structure of their ears).
Southall et al. (2007) propose precautionary noise exposure criteria for injury. Those criteria are currently the best available and their use is recommended. When compiling a risk assessment, a section specifically detailing noise assessment must be included. This should cover:
- Duration and frequency of the activity, as increased exposure is more likely to cause a disturbance offence.
- Intensity and frequency of sound and extent of the area where injury/disturbance thresholds could be exceeded, as chronic noise exposure increases the risk of a disturbance offence.
- Combination effects – the presence of other concurrent, preceding or subsequent activities, activities may have an accumulative effect increasing the risk of disturbance.
- Species specific noise criteria as outlined by Southall et al (2007) use of these criteria aids in risk assessment when EPS are identified in a proposed area of activity.
- Mitigation measures, there may be measures that limit the noise levels, duration and frequency of the activity, thus reducing risk.
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