Abstract
The regulation of noise from offshore activities in the UK requires a metric allowing the behavioral effects on underwater animals of man-made underwater noise on a wide range of species to be objectively assessed. The dBht(species) metric is a pan-specific metric incorporating the concept of ‘‘loudness’’ by using a frequency-weighted curve based on the species’ hearing threshold as the reference unit for a dB scale. A large number of controlled laboratory measurements have been made of the avoidance of a range of idealized noises, using fish with greatly different hearing as a model. Additional data, of many thousands of individuals, has been obtained by re-evaluation of fish avoidance of a large acoustic fish deflection system at an estuarine power station. All data, irrespective of source or species, indicate a dependence of avoidance reaction on the dBht(species) level. The data indicates three regions, ‘‘no reaction’’ below 0dBht (i.e., below the species’ threshold of hearing), a ‘‘cognitive avoidance’’ region where increasing numbers of individuals will avoid the noise from 0 to 90 dBht, and ‘‘instinctive reaction’’ at and above 90 dBht where all animals will avoid the noise. This probabilistic model allows the behavioral impact of any noise source to be estimated.
Published Version
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