In air, noise is well recognised as a pollutant. This is a view which is increasingly being applied to underwater noise. Three effects of underwater sound on fish and other marine mammals are of major significance:
- Direct harm to marine mammals, fish and other aquatic fauna, either physically or by causing changes in their normal behaviour
- Indirect harm via effects on food species (e.g. on marine mammals when fish are driven away)
- The commercial effect of localised depletion of exploited fish stock
In practice the consequences of the former two effects are largely emotive, and the third financial; all three may be litigational. All are of significance and any one can cause vigorous public reaction, causing blasting to be delayed, subjected to severe financial penalties or to be cancelled.
In order to provide an objective and quantitative assessment of the range and severity of any environmental effect from blast, it is necessary to be able to estimate four parameters. These are:
- The source level (i.e. level of sound) generated by the explosive.
- Transmission loss, that is, the rate at which sound from the source is attenuated as it propagates.
- The effect threshold, that is, the level of sound at which a particular effect such as death, injury, or avoidance of a species occurs.
- The population density for a given species.
With the increasing awareness of environmental effects the requirement to demonstrate that environmental effects have been minimised is increasing.