FEATURE | Exposure to magnetic fields from subsea cables slows down haddock larvae, new Norwegian study finds

Photo: Institute of Marine Research/Alessandro Cresci

Haddock larvae swam more slowly after being exposed in the laboratory to magnetic fields similar to those created by undersea cables connecting offshore wind farms, Norway’s Institute of Marine Research (IMR) said recently.

Offshore wind farms and other marine renewable energy facilities are connected by submarine high-voltage cables. The IMR said these cables produce magnetic fields that can affect marine organisms that swim or drift near the cables – particularly fish larvae that have less ability to swim away from the cables.

The IMR added that these possible impacts could be particularly relevant for fish larvae, which have limited capacity to swim away from the cables. However, whether there is an effect on fish larvae is currently unknown and being addressed by ongoing research.

In their most recent study, a research team at IMR focused on impacts on haddock – an ecologically and commercially important species.

Reduced swimming activity

“We wanted to understand whether haddock larvae, which will drift in areas where offshore wind turbines are planned, are affected by magnetic fields in the intensity range of those generated by the subsea cables that connect the turbines,” says Alessandro Cresci, a postdoctoral fellow at IMR.

The researchers set up an experiment that simulated a scenario where fish larvae swam or drifted past an undersea cable. The behaviour of the larvae was filmed and analysed.

“We found no evidence of attraction to or repulsion from the magnetic field,” Cresci said of the findings. “However, the exposure reduced by more than half the swimming activity of the great majority of the haddock larvae, and substantially reduced their acceleration. This reduction in swimming activity could affect the dispersal and survival of haddock larvae in the wild.”

Swims according to its own compass

In earlier research, Cresci and his colleagues found that haddock larvae do not just drift passively with the current; rather, they swim in a north-westerly direction, following an internal magnetic “compass.”

The IMR said this directional swimming plays a role in determining where the newly hatched larvae end up after spawning. Therefore, if their swimming activity is reduced as the larvae drift past subsea cables, this could impact their dispersal and lower their chances to survive.

“For this reason,” added Cresci, “we wanted to understand whether haddock larvae, which will drift in areas where offshore wind turbines are planned, are affected by magnetic fields in the intensity range of those generated by the subsea cables connecting the turbines.”

Realistic simulation in a test tank

The experiment was carried out in a special tank built for the purpose, with electric coils that could induce magnetic fields in one half of the tank. The intensity of the magnetic field was the same as from ordinary subsea cables.

The set-up thus gave a realistic imitation of what larvae will experience when they swim or drift near an undersea high-voltage cable in the wild.

“We placed the larvae one at a time in the middle of the raceway and observed their behavior for 15 minutes. Half of the larvae could freely swim between the high and low magnetic field zones.”

Half of the larvae were exposed to the magnetic field; the rest were observed under similar conditions, but with the electric coils switched off, so that they were only exposed to the natural magnetic field of the earth. These served as controls in the experiment.

The experiment was conducted in the dark, with no visual cues that could influence the behaviour of the larvae. The behaviour of the larvae was recorded using an infrared-sensitive camera.

Clear differences

The haddock larvae showed clear differences in exploratory behavior: A minority (20 per cent) of the larvae were highly exploratory and swam back and forth in the raceway tank. Most (80 per cent) of the larvae were non-exploratory and kept to one side of the raceway tank. This pattern of individual differences in behavior has been observed in several species of fish.

The effect was different between the two groups:

The exposure to magnetic fields in the range of those produced by high voltage subsea cables reduced the swimming speed of non-exploratory larvae by more than half (60 %) compared to the controls. Their acceleration was also strongly reduced (by 38%).

There was no such effect on the exploratory group of fish.

Unique and important findings

This experiment on haddock larvae is part of a larger research project on the impacts of offshore wind farms on fish larvae. The project is assessing the impacts of operational noise from wind farm turbines and magnetic fields from subsea cables on fish larvae.

In a similar study published earlier this year, the IMR team found no significant effect of magnetic fields on larvae of lesser sandeel (Ammodytes marinus), a key species in the North Sea ecosystem. The researchers plan to do an analogous experiment on Atlantic cod larvae.

In addition, they have carried out unique research on the impacts of low-frequency sound in the intensity range of those produced by the turbines on marine fish larvae.

“Our results provide some of the first evidence of the possible ecological future impacts of this expansion [of the offshore wind industry],” said Cresci. “This type of research should be taken into consideration when evaluating the possible implications of this further industrialisation of the sea for marine life.”

Click here for more news and gear stories, feature articles, and vessel reviews as part of this month’s focus on fishing and aquaculture.

Baird Maritime

The best maritime site on the web. The sea's our scene!