Seals 'feed' at offshore wind farms, study shows

Harbour seal (Phoca vitulina) Some harbour seals appeared to preferentially forage at offshore wind farms

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Some seals prefer to forage for food at offshore wind farms, a study suggests.

Researchers found a proportion of GPS tagged harbour seals repeatedly visited wind turbines in the North Sea.

They deduced the mammals were attracted to these structures - which may act as artificial reefs - to hunt for prey.

"As far as we know this is the first study that's shown marine mammals feeding at wind farms," said research team member Dr Deborah Russell from the University of St Andrews, UK.

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The team's findings are detailed in a correspondence article published in the journal Current Biology.

Dr Russell and colleagues tracked dozens of harbour - or common - seals (Phoca vitulina) and grey seals (Halichoerus grypus) living around the British and Dutch coasts of the North Sea. They observed 11 harbour seals visiting wind farms - Sheringham Shoal in the UK and Alpha Ventus in Germany.

"Out of the individuals that we tagged a proportion of them preferentially went to these [wind farm] structures," Dr Russell told BBC Nature.

A number of the mammals moved in a "grid-like" pattern, making straight lines between the turbine bases.

Dr Russell explained: "The animal basically travels from wind turbine to wind turbine, almost like he's checking out, 'OK is there any foraging opportunities at this turbine?' And then he stays there for quite a long time, presumably if there are foraging opportunities."

Seal grid map at Sheringham Shoal wind farm One harbour seal made a grid-like pattern, suggesting it was foraging at the structures

The study also found seals from both species visited man made pipes along the sea floor, which are also thought to act as artificial reefs and foraging sites.

The researchers do not know what species of prey the seals are eating at these hunting grounds. But they may be attracted by fish such as cod or whiting which in turn feed on invertebrates living on the reefs.

Dr Russell said more research was needed to understand the ecological consequences of seals' behaviour around wind turbines.

"There are some issues of course with having animals more in the vicinity of anthropogenic activities, because you've got maintenance vessels in the area, you've got some noise from the wind turbines, so that could be negative.

"But on the other hand it's obviously quite successful in terms of foraging for these individuals, because they're choosing to go back to these anthropogenic reefs time after time," said Dr Russell.

Harbour seal fitted with a GPS phone tag GPS tags allowed the scientists to monitor the seals' movement patterns in detail

The Marine Conservation Society charity, which was not involved in the study, said it was "not surprising" if seals feed around offshore wind farms because the structures are often built on sand flats that are "also important seal breeding, pupping and feeding sites".

A spokesperson for the charity added: "It may be that engineering structures provide more opportunities for predators such as seals in foraging for food, although this doesn't necessarily mean that the structures make an area more productive - seals have been present in significant numbers in the areas studied already."

The team behind the new study now want to find out whether or not wind turbines' artificial reefs have resulted in an increase in number of prey species.

"If [wind turbines] increase the number [of prey species] then that may be a good thing in terms of they're providing foraging opportunities for seals," said Dr Russell.

"But if they simply concentrate the number of prey... it means that instead of being distributed sparsely throughout the environment, they're actually being concentrated and very vulnerable to being 'hoovered' up by predators. So that could actually have a negative effect on those prey species."

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