Researchers tracking the movements of seals discovered that the flipper-wielding predators are drawn to offshore wind farms and underwater pipelines. These kinds of manmade structures might serve as artificial reefs and delectable hunting grounds, according to a new study published in Current Biology this week.
A team led by Deborah Russell from the University of St. Andrews tagged over 100 harbor seals (Phoca vitulina, pictured) and gray seals (Halichoerus grypus) on the British and Dutch coasts of the North Sea using GPS tags attached to their fur at the back of the neck.
Their data showed 11 harbor seals regularly visiting two active wind farms: Alpha Ventus in Germany and Sheringham Shoal in the southeast U.K. An aerial view of Sheringham Shoal is pictured here.
In some cases, the seals traveled in grid-like movement patterns as they appeared to forage from one turbine to another, checking each out for fish. “I was shocked when I first saw the stunning grid pattern of a seal track around Sheringham Shoal,” Russell recalls in a news release. “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.”
In this video, you can see four of the 13 trips made by a single harbor seal to Sheringham Shoal. White points denote the turbines and substations. The seal’s track is shown in red with the yellow pointer updating every half an hour of the track.
Furthermore, both gray and harbor seals were observed hanging out near subsea pipelines. Two seals in the Netherlands encountered a section of pipeline and followed it on multiple trips, for up to 10 days at a time.
“Only a small proportion of our study seals utilized wind farms or pipelines,” Russell says. “At present these structures cover a small proportion of the extent of the at-sea distribution of seals. As wind farms become more extensive, many more seals will likely be affected.”
The team is working on understanding the population consequences of developments planned for the future. The turbines might be increasing the number of prey species, or on the other hand, they might only be concentrating the number of prey. If that’s the case, “instead of being distributed sparsely throughout the environment, they’re actually being concentrated and very vulnerable to being ‘hoovered’ up by predators,” Russell tells the BBC. “So that could actually have a negative effect on those prey species.”
Images: Current Biology, Russell et al. (top) & Mike Page (middle)
Video: Current Biology, Russell et al