A dissertation by Wageningen University & Research published on 28 August 2026 examines how electromagnetic fields from submarine cables affect sharks and rays. Its central finding is neither a blanket all-clear nor evidence of major harm: the animals did not strongly avoid realistic fields in the experiments, but showed subtle behavioural changes depending on species, life stage and sex.
As offshore wind power expands in the North Sea, so does the network of power cables on the seabed. These cables generate electric and magnetic fields. Humans do not notice them, but sharks and rays naturally use such stimuli to find prey, orient themselves, navigate and interact with members of their own species. Annemiek Hermans therefore asks whether the additional fields could become a relevant ecological stressor.
Four wind farms and two model species
The work combines an ecological risk assessment with field observations and controlled experiments. Environmental DNA was studied for two years in four operational offshore wind farms. The team also tested the small-spotted catshark and the thornback ray at different life stages, from embryos and juveniles to adults.
DNA from five cartilaginous-fish species was detected in the wind farms. This argues against the idea that wind farms and their cables completely exclude sharks and rays across large areas or generally block migration. An eDNA detection only shows that a species was present in the area, however. It cannot reveal small behavioural changes or separate the effect of an individual cable from other features of a wind farm.
Thornback ray embryos moved more
Thornback ray embryos were chronically exposed to fields associated with alternating current during development. Hatching success, development time and weight at hatching did not differ clearly from the control group. The exposed embryos did, however, move more. This additional activity could consume energy and perhaps increase the risk of detection by predators in the wild, although the experiment did not directly measure those ecological consequences.
Small differences in body measurements also appeared after hatching. During the subsequent growth phase, the data suggested slightly reduced growth in rays and a temporary increase in size in catsharks. After hatching, however, the researchers found neither clear stress responses nor major changes in swimming behaviour attributable to the earlier exposure. The effects were small and could be obscured by natural variation in the wild.
Adult animals did not avoid the fields
For adult small-spotted catsharks, spatial field gradients simulated crossing a submarine cable. Under neither alternating-current nor direct-current fields did the animals show strong attraction, avoidance, startle responses or altered use of space. The sharks were less active overall under direct-current exposure, but moved faster when they did swim.
Thornback rays likewise showed no clear attraction or avoidance. A finer behavioural analysis did reveal differences between the sexes: under alternating-current fields, females spent less time inactive and switched more often between behavioural states, whereas males were more frequently inactive under both alternating and direct current. Some responses therefore ran in opposite directions, so results from one species or sex cannot simply be transferred to other cartilaginous fishes.
A choice experiment with juvenile catsharks also found no avoidance of the field and no change in their choice between bare and mussel-covered substrate. The animals were only slightly more often inactive where mussels and the electromagnetic field occurred together. Once again there was no clear barrier effect, but a small signal in the activity pattern.
No all-clear for exposure lasting decades
The individual changes seem small. However, submarine cables often remain in operation for more than 40 years, while the number and spatial extent of the fields increase with additional wind farms. So far, little is known about whether animals habituate to the stimuli, whether repeated exposures accumulate, or whether they have a greater impact together with fishing, habitat change, and warming.
There are also methodological limitations: Controlled tank experiments only partially replicate the currents, foraging, migrations, and the many simultaneous stimuli of the North Sea. The experiments focus on two demersal species. Particularly migratory sharks, large bottom-dwelling rays, spawning grounds, and nurseries may have different exposure patterns.
What this means for offshore wind power
Hermans sees no reason in the results to fundamentally delay the expansion of offshore wind power. The dissertation instead recommends optimizing cable and grid design, avoiding sensitive habitats in small-scale route planning, and continuing to monitor the impact under realistic operating conditions. Research should prioritize species and life stages that remain on the seabed for a long time or cross cable corridors particularly frequently.
The official WUR summary of the PhD research interprets the findings with similar caution: dramatic short-term effects appear unlikely for the species studied, but subtle long-term consequences cannot yet be ruled out. The decisive question is therefore not only whether an animal immediately flees, but whether small changes across repeated encounters affect growth, energy use or migration.
The Isle of Man basking shark hypothesis remains open
Haitauchen recently reported on the debate about electromagnetic fields and basking shark sightings off the Isle of Man. The new dissertation provides important context but does not resolve that hypothesis. It mainly examined bottom-associated species in the North Sea, not basking sharks or cable routes around the Isle of Man. The absence of a barrier effect in catsharks and thornback rays therefore does not show that migrating basking sharks remain unaffected.
The most important progress lies in this differentiation. Electromagnetic fields from subsea cables are perceivable by sharks and rays, but perception does not automatically mean avoidance or acute harm. The measurable responses are subtle and varied. Precisely for this reason, future assessments must consider life stage, species, sex, habitat, and the duration of exposure together.
