Delve into how different animal behaviours are changing due to anthropogenic noise under the ocean's surface.
Impacts of Noise Pollution:
Hearing:
Animals that are in close range to the source of noise may suffer either temporary or permanent damage to their hearing. TTS and PTS are detailed in the 'noise pollution' blog, though a brief overview is that TTS is similar to the hearing loss humans may experience after a loud concert, and PTS is when sound waves are so strong they permanently damage the auditory organs. PTS and TTS cause reduced health and survival, and can affect individuals in a community, though the reality is they will most likely affect entire populations in areas where there are high densities of ship travel or construction.
Masking:
Anthropogenic noise can overlap with natural sounds and communication with cetaceans, and therefore pose huge risks interfering with communities and the transfer of information. This may lead to an increase in predation if they cannot warn one another, or even increased risk of vessel-animal collisions if they cannot locate the source of the noise. In one study, hermit crabs allowed a simulated predator to approach closer than usual before hiding, as the noise was masking and distracting their normal behavioural responses.
Behavioural Changes:
Because sound travels further and quicker underwater, anthropogenic noise can increase stress and reactions that may alter critical functions such as feeding, socialising and resting whilst an animal is attempting to move away from the noise. Over time, this will have long-term effects on the individuals health and energy. If this noise affects entire communities, there is likely to be a decrease in reproductive rates due to higher stress hormones within the group.
Disruptions on feeding:
When stressed, marine animals tend to decrease their food intake, whilst increasing their metabolic rate. Because of this, there is a decrease in body mass and survival rates.
Migratory Changes:
It has been documented in some areas that the occurrences of animals such as Orcas declined significantly in areas that had AHDs (Acoustic Harassment Devices) installed, and mesopelagic species moved to deeper waters during seismic shooting seasons - showing a conscious decision to be further from the noise.
Stress and Health:
Anthropogenic noise has the potential to trigger the stress response in mammals - which can have devastating effects. Cetaceans are susceptible to the physiological challenges that come with deep diving, fasting, and thermoregulation, and they are all controlled by the endocrine system. When the stress response is triggered, this can dramatically impact the survival of an individual in those conditions.
Beaked whales are particularly susceptible to these impacts. A recent study found that beaked whales' physiology means rapid surfacing from sound exposure - causing gas-bubble disease, also known as decompression sickness, and explain the morbidity and mortality in mass strandings seen after sonar trials.
Conservation Efforts
Mitigation efforts to reduce noise include:
- Pile screwing instead of pile driving,
- Additional sound reduction gear,
- Safety zones - if animals are sighted within these zones, machinery is turned to low power or shut off until the zone is clear again. This has been the most effective mitigation effort so far, and are closely monitored by mammal observers using binoculars.
- Passive acoustic monitoring - only useful for vocalising animals.
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