Oceans of noise - Whale and Dolphin Conservation Society

5.3 Longer-term impacts
Noise is clearly biologically significant if it induces long-term abandonment of an area important
for feeding, breeding or rearing the young, as it may lead to reduced fecundity, carrying capacity,
or both (Richardson 1997). Consequences will not become apparent until more research is
conducted into the long-term effects of noise pollution.
5.3.1 Sensitisation and habituation
Sensitisation occurs, when, for example, an animal has been exposed to a painful level of noise
from a particular source, causing it to avoid the source. Habituation occurs when the stimulus is
no longer novel although adverse consequences may still be associated with it. Weilgart (1997)
noted that damage from very intense sound might not be obvious at sea, especially in the shortterm.
Marine mammals are intractable animals to study in the wild and auditory damage is almost
impossible to detect in free-ranging large whales. Gradual deafness might easily be
misinterpreted as a growing tolerance or habituation to noise.
5.3.2 Stress
Stress is a condition often associated with the release of adrenocorticotrophic hormone (ACTH)
or cortisol. It is recognised that noise and disturbance lead to an increase in activity of glands
producing these hormones (Welch and Welch 1970). Increases in these hormone levels are
usually associated with changes in behaviour, such as increased aggression, changes in respiration
patterns or altered social behaviour. However, noise-induced stress may be present but does not
necessarily cause overt changes in behaviour (Thomas et al. 1990).
Prolonged noise-induced stress can lead to debilitation, e.g., in fish and invertebrates, prolonged
exposure can induce infertility, pathological changes in digestive and reproductive organs and
reduced growth (Banner and Hyatt 1973; Lagadere 1982). Prolonged exposure to high levels of
noise and the resultant chronic activation of stress-related hormonal complexes could lead to
harmful effects in cetaceans (Seyle 1973; Thomson and Geraci 1986; St Aubin and Geraci 1988),
for example:
Arteriosclerosis (Radcliffe et al. 1969)
Nutritional problems (Smith and Boyd 1991)
Stomach ulceration (Brodie and Hanson 1960)
Suppression of reproductive function (Moberg 1985)
Reduction in resistance to infection (Cohn 1991).
Decrease in life expectancy (Small and DeMaster 1995)
5.3.3 Physiological damage to tissues and organs
The sudden pressure changes cause by intense noise can result in actual physiological damage.
Ketten (1995) divides the physiological effects of intense noise into two categories:
1) Lethal blast injuries;
2) Sub-lethal acoustic trauma.
Lethal effects are those that result in the immediate mortality or serious debilitation of animals in
or near an intense noise source (e.g. submarine blasting). Sub-lethal effects occur when sound
57