Oceans of noise - Whale and Dolphin Conservation Society

Increased vulnerability to disease
Increased potential for impacts from negative cumulative effects (e.g. chemical pollution
combined with noise-induced stress)
Sensitisation to noise (or other stresses) – exacerbating other effects
Habituation to noise – causing animals to remain close to damaging noise sources
Indirect Effects
Reduced availability of prey.
Increased vulnerability to predation or other hazards, such as collisions with fishing gear,
strandings, etc.
5.2.2 Masking of biologically important sounds
Anthropogenic noise can be of such a frequency and intensity as to clash with and cover up
biologically important sounds, making them undetectable by cetaceans. Biologically important
sounds include:
Echolocation clicks for finding prey;
sound cues from conspecifics, prey or predators;
courtship or group cohesion vocalisations;
those for navigational aid; and
calls between mothers and calves.
Masking these sounds will make it more likely that cetaceans will be unable to feed; more likely
that they will be attacked by predators; and unable to socialise, reproduce or rear their young
properly. Thus, calf production and health in cetacean populations would likely be reduced and
mortality rates increased.
In order for a cetacean to detect and respond appropriately to sounds, it must be able to locate
them. It has been generally assumed that marine mammals will respond to loud noises by moving
away. However, this response requires them to be able to both localise the source and recognise it
as a threat. Unknown noises could invoke responses of curiosity or, if they were mistaken for a
competitor (for example, another noisy male), even aggression.
5.2.3 Social disruption
Social disruption brought about by noise may be especially important if mother/calf pairs become
separated. Animals resting or with small calves could be weak and vulnerable to predation and
exhaustion (McCauley et al. 1998). The potential continual dislocation of these animals may have
serious consequences at the population level.
5.2.4 Depth of animal
A cetacean may experience different sound levels depending on the depth at which they are
encountered. Sound levels to which marine mammals are exposed while near the surface and
visible, are often unrepresentative of those received when they are out of sight below the surface.
For some underwater sources, especially those emitting low frequency sound, pressure release
and Lloyd mirror effects may cause lower levels near the surface.
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