Over the past 20 years it has become increasingly evident that noise from human activities in and around the marine environment is likely to have an impact on the marine species in that area and beyond. Unlike light and other stimuli, sound is transmitted very efficiently through water with sound often being detectable underwater at distances many times that which would be expected with noise in air. Piling noise can be detected at a range in excess of 100km in water of 30m and this extends considerably further in deep waters.
The efficiency of sound propagation under water allows marine animals to use sound as a method of communication, sometimes over long distances and to sense the presence and location of objects including prey. Marine animals may obtain a great deal of information about their environment by listening to the sounds from natural sources. Examples may include the sound of surf indicating the presence and direction of the shoreline, ice noise and sounds from predators.
The impact on marine life from manmade noise varies considerably according to the source of the noise and the species considered. Continuous noise (such as from shipping or dredging) can have the effect of raising the background noise level preventing detection of other sounds important to the animal whilst high level impulsive noise (such as from piling or seismic surveys) can have a significant behavioural effects and possibly cause fatal injury.
As marine animals have evolved to use sound in different ways, the assessment of the impact is usually species specific. Many marine mammals and fish have highly evolved hearing and use sound extensively to navigate, communicate and find food. Other species that migrate up rivers (such as salmon) have relatively poor hearing as it is of little use in the turbulent river environment. Each species will therefore have a different response to changes in the noise environment adding complexity to an assessment of the impact. The dBht (species) proposed by Dr Nedwell is a criteria that seeks to assess the impact of noise in a biologically meaningful way.
Research into the impact of noise on marine life has tended to focus on the impact of specific noise events (piling, blasting, SONAR etc.) on individuals in the area. These studies have resulted in various criteria being proposed for assessing the likely impact on fish and marine mammals in terms of behavioural changes, physical effects and likelihood of injury for a given noise exposure. However there remains a significant gap in understanding the cumulative impact of the overall increase in marine noise levels.
Therefore more research is needed to gain an improved understanding of the impact of a general increase in noise levels across the marine environment alongside the specific impact of development activity. Given the range over which sound can propagate activity in one may have an impact many miles from the source and beyond national boundaries and therefore requires an international approach. We welcome the opportunity to be part of this process.
 Equasis Statistics – The world fleet 2005, The world fleet 2010 – European Maritime Safety Agency, 2011 http://www.emsa.europa.eu