The water around the turbine leg looked empty.
It always does, from the surface of the North Sea in winter.
But a bottle dipped into the grey water held something invisible: fragments of DNA shed by an animal few people expected to find there.
The working assumption was that the turbines had pushed the sharks away.
The water said otherwise.
Why a wind farm might shelter sharks instead of pushing them out
The logic that said sharks and rays would avoid offshore wind farms was never unreasonable. Construction noise, vessel traffic and the electromagnetic fields around subsea power cables all look like plausible reasons for an animal that hunts by sensing faint electrical pulses to swim somewhere quieter. Until this work, the active presence of sharks and rays inside Dutch wind farms had not been confirmed from the water itself.
The researchers offer a competing explanation, and they present it as a possibility rather than a settled mechanism. Trawling and other seabed disturbing fishing are prohibited inside wind farm boundaries, which allows bottom habitats to recover. The hard substrate on turbine foundations is colonised by mussels and barnacles that draw fish, and those steadier habitats, the team argues, could benefit vulnerable species.
The samples themselves record presence, not cause. Water carrying shark DNA tells you an animal passed through a place; it does not tell you what brought it there.
The species that showed up inside the turbine fields
Across four Dutch offshore wind farms, the analysis identified five distinct species of elasmobranch: three rays and two sharks. The thornback ray was the most frequently detected, present year round at three of the four sites. The starry smooth hound and the blonde ray turned up across multiple seasons and multiple sites.
Then there was the basking shark in midwinter. Its DNA was detected at the Hollandse Kust Zuid wind farm during winter, an unusual record for Dutch waters that the team says offers insight into the species’ seasonal movements.
It is a presence record rather than a count, and nobody saw the animal itself.
What 436 bottles of seawater can and cannot say
The scientists did not net or tag anything. They drew environmental DNA straight from the water, filtering 436 seawater samples collected over two years at Borssele, Hollandse Kust Zuid, Luchterduinen and Gemini, and combining new fieldwork with data from The Rich North Sea programme. The results were published in the journal Ocean & Coastal Management. Lead author Annemiek Hermans has likened the method to “finding a fingerprint” in the water.
The farms span a wide stretch of the southern North Sea. Hollandse Kust Zuid alone holds 139 turbines and sits between about 11 and 22 miles off the Dutch coast.
What the method cannot do is count individuals, measure how long an animal lingered, or show whether it changed course when it crossed a power cable.
Where the finding holds and where it gets complicated
The electromagnetic field question runs in both directions, and the same six year ElasmoPower programme is testing it in tanks as well as at sea. In those experiments, adult small spotted catsharks showed no strong attraction or avoidance under AC fields, while DC fields produced subtler changes, including reduced activity. Work on migratory species at energy infrastructure is expanding on the same logic: document presence first, then ask what the infrastructure is doing to behaviour.
Hermans has urged caution about reading the result as a conservation victory, saying researchers “must tread carefully,” and warning that opening these zones to bottom trawling would remove whatever protection they currently provide. The refuge effect is an argument being built, not a conclusion already banked.
DNA traces alone cannot separate an animal that thrives inside a wind farm from one that merely swims through it.
What a recovering seabed inside a wind farm boundary means next
Offshore wind is still scaling fast in exactly the seas where these species have been fished hardest. A global industry body reported 83 GW of installed offshore capacity worldwide at the end of last year, with annual additions forecast to climb from 8 GW to more than 34 GW by 2030. Every one of those projects comes with an exclusion zone attached.
Finding sharks and rays inside active wind farms, year round and in winter, suggests those boundaries may be doing ecological work nobody designed them to do. Research into wildlife at energy infrastructure is growing alongside the buildout, and the answers will shape what a developer monitors and what a regulator asks for.
The basking shark that left its DNA in a winter water sample was not expected there. That it was is the most honest summary of what this study found, and probably the most useful one too.
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