Noise from the construction of offshore wind turbines could be damaging the hearing of harbour seals around the UK, researchers have found.
A study by ecologists from the University of St Andrews found that around half the seals they analysed during a construction project in England were exposed to noise levels that exceeded hearing damage thresholds.
Overall, experts said, little is known about the impact of construction noise on sea mammals’ hearing and they have called for more research to be carried out into the issue.
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.
According to the researchers, there are currently 1,184 offshore wind turbines around the coast of the UK, between them generating around 4GW of power. The next round of construction, which began last year, will see hundreds more turbines installed to generate a further 31GW.
Conducting their study, the St Andrews team attached GPS data loggers to 24 harbour seals while offshore wind turbines were being installed in the Wash in 2012. The data loggers collected information on the seals’ locations and their diving behaviour.
The researchers then combined this data with information from the wind farm developers on when pile driving was taking place to produce models which predicted the noise to which each seal was exposed.
The model revealed that half of the tagged seals were exposed to noise levels which exceeded hearing damage thresholds, the research team said.
Although some information exists about the effects of noise on harbour seals’ hearing, very little is said to be known about the impact of the pulsed sounds produced by pile driving. But data on the effect of noise on humans and other terrestrial species shows that powerful pulsed sounds can damage mammals’ hearing.
Lead author of the study, Dr Gordon Hastie of the university’s sea mammal research unit, said pulsed sounds are “some of the most powerful man-made sounds produced underwater, noise capable of travelling large distances underwater”.
He said: “Like most marine mammals, harbour seals have very sensitive underwater hearing at a much broader range of frequencies than humans.
“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.”
The university said the team’s results are important because seals are protected under European law and anything which might affect their conservation status needs to be assessed prior to the construction of wind farms.
Dr Hastie said: “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.
“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.
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