Human made noise, also called anthropogenic noise, is rising in many environments due to the increase in transportation and the exploration for and exploitation of energy sources.
North Western Australia, in particular as the most active area of the country in terms of oil and gas exploration and coastal construction activities, is filling WA’s coastline with added background noise.
In the extreme, anthropogenic noise can destroy the vulnerable sensory tissues, in the inner ear and the lateral line systems of fishes.
This may ultimately lead to death if the animals lose their ability to hear or detect hydrodynamic changes.
Noise can also be a source of acute or chronic stress, which may affect behavioural and sensory functions.
Besides, a loud sound can mask important biological sounds, essential to marine organisms in communication, finding prey and mates and detecting predators.
More than 100 species of sharks and rays live in WA waters, ranging from the tiny pygmy shark (Euprotomicrus bispinatus) to the iconic whale shark (Rhincodon typus), the world’s biggest fish.
Sharks, like bony fishes, possess an inner ear and a lateral line, which are sensitive to underwater vibrations and sounds.
Sensitive to Very Low Frequencies
Compared to marine mammals, sharks have a very narrow hearing range but are known to be particularly sensitive to very low frequencies.
This hearing range overlaps with most of the anthropogenic sound produced by seismic airgun arrays, dredging, pile driving and shipping.
Some sharks are migratory and can potentially leave a disturbed area, for example great whites (Carcharodon carcharias), tigers (Galeocerdo cuvier) and whale sharks.
However most of the species, such as wobbegong (Orectolobidae), bamboo (Hemiscylliidae) and Port Jackson sharks (Heterodontus portusjacksoni), stay in a single location or patch of reef or change habitats only when they reach a critical part of their lifecycle like most reef sharks do.
Sound pollution represents a particular threat for those sedentary sharks, as they would typically not leave the area during a high intensity sound event.
In an effort to fill these vital knowledge gaps, the Neuroecology Group which is part of the University of Western Australia Oceans Institute and School of Animal Biology is studying the effects of sounds on sharks.
Their first strategy will be to assess their sensitivity to sound such as what frequencies and intensities the different species react to, with electrophysiological techniques in the laboratory.
Photo: Leszek Leszczynski/flickr