As wind farms march out into coastal waters to meet energy demands, seals are learning to use them like local grocery stores, scientists say. A few wily individuals have been spotted prowling the grids of turbines, checking for fish congregating around individual pillars and stopping to feast when they find them.
Scientists discovered this using GPS monitoring to track the movements of approximately 200 animals — including both gray and harbor seals — near offshore wind farms in Germany and Britain. Though only a handful of seals ventured into the farms, those that did often returned repeatedly and appeared to forage around wind towers, scientists said in a study published Monday in the journal Current Biology.
The routes the seals took through the farms made it clear they knew what they were looking for, said the researchers, led by Deborah Russell of the University of St. Andrews in Scotland. The video below shows how the animals swam straight and fast between towers, then slowly and sinuously near certain turbines, the way seals behave when they eat.
"Some of the animals were spending a couple of hours at a turbine, and then moving to the next turbine and spending a long time there," Russell said. In total, certain individuals spent days within the farms.
The scientists also found that a few seals followed undersea pipelines, sometimes for up to 10 days at a time, and appeared to find food there too.
Aside from capitalizing on man-made structures, these seals did not stand out from the crowd in any peculiar ways; they also foraged successfully in the open ocean and appeared healthy when the scientists handled them to fit their GPS devices.
Though this study marks the first time scientists have documented changes in seal behavior around wind farms, the discovery that such installations might change the ecology of the ocean is not entirely unexpected. Researchers have long recognized that so-called artificial reefs — including oil rigs, shipwrecks and purpose-built cement "reef balls" — provide new habitats for plants and animals that usually make their living on rocks and seafloor, and for the fish that eat them.
That larger predators might discover this bounty may only be a matter of time.
In the study, only about a dozen seals explored the farms, which cover a minuscule area of the North Sea, and fewer still made a habit of doing so. But the scientists say many more could frequent the structures because they only tagged a tiny sliver of the total seal population. (There are about 55,000 harbor seals and 65,000 gray seals along just one stretch of the British coast.)
The researchers also suspect more seals will get wise as the artificial reefs mature and become more established. Both farms are less than 5 years old.
"One of the most important things is to quantify how prevalent this behavior is in the population of seals," Russell said.
But whether these changes represent a long-term benefit or a threat to seals remains unclear. If the new environment winds up boosting the overall population of prey species, it may bolster seal populations as well. But if wind farms simply concentrate fish inside their borders, the effects could be more complex.
"We still don't know for many species whether these are simply congregating devices," Russell said. "If it's just a concentration, and prey species are being Hoovered up by seals, that would be bad for the prey."
Russell can't say whether this would ultimately affect seal populations; the animals typically eat a diverse diet and don't depend too much on any one source of food.
She also cited other concerns about seals spending more time in wind farms, such as increasing their exposure to noise pollution from the turbines themselves and interactions with maintenance vehicles.
In the end, the scientists say it's important to get to the bottom of the "production vs. attraction" debate and how many seals learn to utilize this novel foraging environment, because more offshore wind farms will pop up in coming decades. If planners know how these farms help or hurt marine ecosystems, they can tweak their construction to maximize the positive effects on seals and other marine animals and minimize their costs.