Static magnetic fields reduce swimming activity of Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) larvae

Static magnetic fields (B-fields) are introduced in marine ecosystems by anthropogenic sources such as subsea power cables. Larvae of the gadoids Atlantic haddock (Melanogrammus aeglefinus) and Atlantic cod (Gadus morhua) disperse over the continental shelf and may encounter B-fields, which could alter their behavior. We tested the behavior of 184 gadoid larvae while they were being exposed to a B-field (22-156 mu T), which is in the intensity range of that produced by a high-voltage direct current cable, for a duration of 10 min in a raceway tank. We present a reanalysis of published data on 92 haddock larvae combined with newly collected data on 92 cod larvae tested under the same settings. Exposure did not affect the spatial distribution of the larvae. Both species displayed the same proportion of nonexploratory (78%) and exploratory (22%) individuals. Exposure significantly reduced the average swimming speed of the nonexploratory larvae by 32% and the average acceleration by 30%. Exploratory larvae were not affected. These results indicate that the swimming behavior of a high proportion of gadoid larvae would be reduced by weak static B-fields. Consequences of exposure on dispersal and survival at the population scale awaits further work using biophysical-coupled models.