A harbor seal involved in the study wears a GPS beacon. Current Biology/Russell et al.

Some swim around the turbines in a grid fashion, probably hunting for prey.

The action at offshore wind farms seems to be happening above the waves, with those giant, spinning turbine blades. But there's something interesting going on below, too. Some seals flock from miles around to swim among the turbines' support structures, tracking from one to the other as if completing a grid.

The magnetism of wind farms to marine life is the subject of a study published today in Current Biology describing underwater activity at the U.K.'s Sheringham Shoal, shown here:

(Current Biology/Russell et al.)

Deborah Russell, a marine researcher at the University of St. Andrews, had her team fix GPS trackers to seals living on the coasts of the North Sea. They then sat back and watched as a small proportion of the mammals (11 of 118) made multiple ventures into Sheringham Shoal and also Alpha Ventus, a farm off of Germany. Aside from dodging to and fro among the turbine pylons, some of the seals also showed a fascination with underseas pipelines, in several cases following one in the Netherlands for as long as 10 days.

Russell speculates that they're seeking food at the underseas structures, which can act like artificial reefs with a higher concentration of fish and crustaceans. And a handful of the animals appear to be hunting in an extraordinarily efficient way. 

"I was shocked when I first saw the stunning grid pattern of a seal track around Sheringham Shoal," she says. "You could see that the individual appeared to travel in straight lines between turbines, as if he was checking them out for potential prey and then stopping to forage at certain ones."

This map shows the orderly trajectories of one harbor seal at the Alpha Ventus installation, with dots indicating the creature's location at half-hour intervals:
(Current Biology/Russell et al.)

This must be welcome news for the wind industry. When people talk usually about turbines and animals, it tends to involves some unfortunate critter getting whacked to death by the blades. However, Russell says it's too early to say whether the growing development of oceanic farms will be a boon to seal populations. The research team explains:

The researchers now hope to continue their research to understand the population consequences of the massive planned developments. For instance, no one knows yet whether wind farms increase the total amount of prey available to seals or simply concentrate prey in a new and man-made location, making the prey particularly vulnerable to predation. The researchers say it will be imperative to resolve this uncertainty so that anthropogenic structures can be designed and managed to reduce adverse and increase any positive effects of these structures.

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