Researchers tracking the movements of seals in the North Sea have discovered they like visiting offshore wind turbines.
They fitted a number of harbour - or common - seals (Phoca vitulina) and grey seals (Halichoerus grypus) with GPS trackers. They have published their findings in Current Biology.
Both species spend time at sea for a few days to a month with visits to land to "haul-out". What the researchers found is that both species tagged in both the UK and Netherlands visited recently constructed wind farms. Not only that, some individuals went in a straight line from one turbine tower to another and hung around each for a bit. Tracks show a perfect grid corresponding to the wind farm and, in one case, another structure. This strongly suggests that they are using the towers to hunt for fish. Some other seals followed the route of undersea pipelines.
Their hypothesis is that these man-made structures are providing artificial reefs. These provide an environment where crustaceans can thrive. Fish gather to feed on them and in turn these are prey for the seals. The researchers are uncertain whether the total number of fish are increasing or are being attracted to these sites while the total numbers remain constant. This will not become clearer until the reefs have had time to get established. In one case, the wind farm had only been installed for a year or two.
If the total number of fish is not increasing, design changes might have to be made to mitigate the concentrating effect. On the other hand if there are more fish, different designs would help provide more foraging place for top predators like seals.