Effects of the electromagnetic field used in hydrocarbon surveys on marine organisms

Abstract

Controlled Source Electromagnetics (CSEM) technology has been used in the exploration for hydrocarbon reservoirs. It consists of an electric dipole source which is towed horizontally 30-50 m above the seabed or 10 m below the surface. As the electromagnetic (EM) signal propagates through the subsurface it may affect marine organisms that are electro- or magneto-sensitive. A device simulating these conditions (corresponding to three different exposure levels, low, strong, near field) was built to test the effect of EM on marine organisms in laboratory conditions.) Sandeel (Ammodytes tobianus) adults were filmed during a 15-minute near-field EM exposure but showed no significant changes in their behavior, nor any increased mortality. Haddock juveniles (Melanogrammus aeglefinus) were first exposed for 15 minutes to either one of the three EM levels then filmed and tested for magnetic orientation. None of the treatments caused mortality in fish. Juvenile haddock showed significant orientation according to the magnetic field but only after exposure to low and strong EM fields. They also showed a significantly reduced swimming speed following exposure to EM with intensities equivalent to distances of 100 (strong) and 1000 m (low) from the source with an average reduction in speed of 24%. Mean instantaneous swimming velocities of haddock decreased from 1.18 pixel/s (control) to 0.86 and 0.80 pixel/s after exposure to low and strong field levels respectively (GLM estimates), representing speed reductions of 27% and 32% after exposure to each respective level. Changes in swimming speed may affect dispersal of juveniles. However, it is unknown whether the decrease was a physiological or behavioural response. Therefore, it is not possible to make unequivocal conclusions about detrimental effects of CSEM at the population level.