Fears raised of damage to seals’ hearing from pile driving for offshore wind turbines 

Laying foundations in the seabed for offshore wind farms is feared to be damaging the hearing of harbour seals around the UK’s coast, according to scientists.

The noise from pile driving during turbine construction could have serious health implications for the marine mammals, ecologists from St Andrews University are warning

They say more research is needed on how noise affects seals’ hearing and into engineering solutions to reduce noise levels. The study is published today in the British Ecological Society’s Journal of Applied Ecology.

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 in 2014, will see hundreds more turbines installed to generate a further 31GW, little is known about the impact of construction noise on sea mammals’ hearing.

The St Andrews researchers 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.

They 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 each seal was exposed to. They compared this with noise levels that other studies show caused auditory damage.

The model revealed that half of the tagged seals were exposed to noise levels that exceeded hearing damage thresholds.

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.

The lead author, Dr Gordon Hastie of the university’s Sea Mammal Research Unit said, “These are some of the most powerful man-made sounds produced underwater, noise capable of travelling large distances underwater.”

He said very little was known about the impact of the pulsed sounds on seals. However, a wealth of data existed on the effect on humans and other terrestrial species, data which showed that powerful pulsed sounds could damage mammals’ hearing.

“Like most marine mammals, harbour seals have very sensitive underwater hearing at a much broader range of frequencies than humans,” said Dr Hastie. “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.”

Seals are protected under European law and any impacts that might affect their conservation status need to be assessed prior to the construction of wind farms.

But Lindsay Leask, Senior Policy Manager, Offshore Renewables at industry body Scottish Renewables, said: “The Scottish offshore wind industry is really only just beginning to deploy technology into the marine environment, but years of environmental surveys, required as part of a rigorous planning process overseen by Marine Scotland, have already been carried out.

“Developers are required to submit incredibly detailed and thorough environmental impact assessments to Marine Scotland, which cover a wide range of subjects, including marine mammals.”