Abstract: Mitigation measures to reduce the risk of injury to whales from loud sound sources are often based on shutting down the sound source if whales are detected visually within a certain safety zone. Visual detection will only detect a proportion of the whales that enter such a zone, and the likely risk reduction achieved has rarely been quanti­fied. A general simulation model is presented which uses data from sighting surveys and diving behaviour to estimate the probability of detection of a surfacing cue. This can be combined with simple assumptions about sound propagation to estimate the proportion of animals that would be subject to sound exposure levels above a certain threshold, with and without mitigation measures in place. This gives an indication of the mitiga­tion efficiency or the level of risk reduction that can be achieved. Results indicate that there will be many cases where using visual observers results in only a very small risk reduction, but these situ­ations may not always be immediately apparent. Without an adequate quantified assessment of the risk reduction, mitigation measures may often be applied inappropriately or result in regulators granting approval for activities on the basis of measures that do little to reduce risk. The simple simulation model is easy to apply but does need to be performed on a case-by-case basis using input data that correspond as closely as possible to the scenario being investigated.

Key Words: underwater noise, MMO, mitigation efficiency, seismic survey

Document Type: Research Article

DOI: http://dx.doi.org/10.1578/AM.41.4.2015.375

Page Numbers: 375-387

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