Harbour seals living close to wind farm construction sites risk hearing problems due to exposure to excessive noise levels, a study has found.
While strict limits for day and night time noise are in place protecting people living in noisy areas, no such measures exist to take care of the well-being of animals - even if those animals are endangered and protected by European law.
As the study by University of St Andrews researchers found, the hearing of some marine mammals could be at risk with the increasing activity of humans in coastal waters.
In particular, the team of ecologists led by Gordon Hastie focused on seal communities living close to places where offshore wind farms are being built. The researchers fitted 24 animals with GPS trackers to monitor their movements near the wind farm construction sites. They were particularly interested to see which seals were in the water close to the sites at times when the noisiest tasks were taking place. Combining the GPS data with construction activity information, the researchers were able to create models predicting individual noise exposure of every animal in the studied group.
The findings were shocking. Half of the seals were exposed to noise levels exceeding the hearing damage thresholds. What makes the matter worse is that seals have far more sensitive ears than humans, capable of intercepting a much wider range of frequencies.
"Like most marine mammals, harbour seals have very sensitive underwater hearing at a much broader range of frequencies than humans,” Hastie said.
"Seals probably use underwater hearing during the mating season and to detect and avoid predators. They may also rely on their hearing for navigation and finding prey."
A deaf seal or a one with impaired hearing probably wouldn't survive for long.
The researchers suggested the wind farm developers may be in fact breaching the seals’ protected status.
Offshore wind turbines are installed using pile drivers - essentially large hammers that drive the foundation posts into the sea bed - which produce short pulsed sounds every few seconds.
It is this type of sound that is of the greatest concern to the researchers. Although some information exists about the effects of noise on harbour seals' hearing, no one has studied the effects of those powerful pulses before. However, comparable data for humans and some terrestrial species suggest that the effects might be serious.
"Our predictions highlight that seals may routinely be exposed to potentially hazardous levels of underwater noise during pile driving, with potential implications for the conservation status of some populations,” Hastie said.
"To reduce these potential impacts, regulators and industry are currently investigating engineering solutions to reduce sound levels at source, and methods to deter animals from damage risk zones in order to potentially reduce auditory damage risk."
The ecologists now plan to make further hearing measurements on seals using special "seal headphones", monitor individual seals' movements at sea, and collect long-term data on their growth, reproduction and survival.