Oceans of noise - Whale and Dolphin Conservation Society

Increased vulnerability to diseaseIncreased potential for impacts from negative cumulative effects (e.g. chemical pollutioncombined with noise-induced stress)Sensitisation to noise (or other stresses) – exacerbating other effectsHabituation to noise – causing animals to remain close to damaging noise sourcesIndirect EffectsReduced 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 soundsAnthropogenic noise can be of such a frequency and intensity as to clash with and cover upbiologically important sounds, making them undetectable by cetaceans. Biologically importantsounds 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 likelythat they will be attacked by predators; and unable to socialise, reproduce or rear their youngproperly. Thus, calf production and health in cetacean populations would likely be reduced andmortality rates increased.In order for a cetacean to detect and respond appropriately to sounds, it must be able to locatethem. It has been generally assumed that marine mammals will respond to loud noises by movingaway. However, this response requires them to be able to both localise the source and recognise itas a threat. Unknown noises could invoke responses of curiosity or, if they were mistaken for acompetitor (for example, another noisy male), even aggression.5.2.3 Social disruptionSocial disruption brought about by noise may be especially important if mother/calf pairs becomeseparated. Animals resting or with small calves could be weak and vulnerable to predation andexhaustion (McCauley et al. 1998). The potential continual dislocation of these animals may haveserious consequences at the population level.5.2.4 Depth of animalA cetacean may experience different sound levels depending on the depth at which they areencountered. Sound levels to which marine mammals are exposed while near the surface andvisible, 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 releaseand Lloyd mirror effects may cause lower levels near the surface.56