Polluted waters: the harms of noise

Fresh and saltwater marine soundscapes are becoming noisier as anthropogenic sounds are introduced into waterways. Before the industrial revolution, the contribution of man-made sounds was minor; but now a greater proportion of noise is attributable to human activity, coming from sources such as sonar, seismic surveys, shipping, and coastal developments like offshore windfarm construction and the operation of oil infrastructure.  

Sound is utilized by marine animals for navigation, communication and foraging. Frequencies produced by anthropogenic sources can overlap with those used in communication – an effect called masking. Masking disrupts the social cohesion of communities and increases predation risk. Marine noise can both subtly and drastically alter behaviour, from minor changes in the length of time spent surfacing to effortful avoidance and escape behaviours. Noise pollution is also known to cause acoustic trauma and temporary hearing loss in whale, fish and squid species. Hearing loss results from a temporary shift in the auditory threshold (the point at which sounds are detected) following exposure to intense sounds.

A new study has found turtles are also at risk of a reduction in hearing sensitivity. Researchers implanted subcutaneous electrodes above the ears of 2 species of freshwater turtle, Trachemys scripta elegans and Chrysemys picta. Before exposing the turtles to any sound, normal hearing ranges were established. Turtles were then momentarily exposed to high amplitude white noise of 50 to 1000 Hz. Return to hearing normality was monitored for the next hour and followed up after 2 days.  

The results showed reptiles are more sensitive to noise than previously believed. Although hearing always recovered, loss lasted between 20 minutes and 1 hour, expect for in a single individual who took multiple days to recover. Even relatively short periods of loss can be detrimental to survival as the inability to detect sounds made by conspecifics or environmental cues may mean predator warnings and vital communications are missed. 

As anthropogenic noise is a pollutant causing major disturbance, efforts should be and are being made to reduce levels. Continuing to develop ocean-based economies, such as shipping and energy, without acknowledging and altering pollution levels will have devastating impacts on marine ecosystems. Approaches can include implementing sound management programs, e.g., alterations to ship designs, and use of technologies, like noise dampening bubble curtains for wind turbines. Simpler approaches can also be taken, for instance setting speed limits and rerouting vessels away from areas of biological concern. There is already evidence to suggest the success of such measures, providing hope that attempts to tackle global industrialization of the ocean may prove a success. Furthermore, sound as a pollutant does not endure in the environment after its source has been removed, meaning practices put in places to reduce noise should have prompt effects.