Burial of submerged power cables would not appear necessary strictly for biological reasons, according to a study funded by the U.S. Bureau of Ocean Energy Management (BOEM), as the electromagnetic fields (EMF) from energized subsea cables neither attract nor repulse fish or invertebrates.
EMF strength dissipated relatively quickly with distance from the cable and approached background levels at about one meter from the cable, according to the three-year study, ”Renewable Energy In Situ Power Cable Observation” , carried out by BOEM’s Pacific Region office and research partners from the University of California Santa Barbara.
Given the rapidity with which the EMF produced by the energized cables diminishes and the lack of response to that EMF by the fishes and invertebrates in this study, the researchers concluded that cable burial would not be necessary solely on the grounds of minimizing the effect on the surrounding fauna.
However, the study concluded that cable burial at one to two meters depth below the seafloor would be an adequate mitigation tool to further decrease potential exposure to EMF.
The purpose of the study was to shed light on the potential effects of energized, seabed deployed, power cables on marine organisms, broadly applicable to planned and future renewable energy projects in the Pacific Outer Continental Shelf (OCS) region and other OCS planning areas, according to BOEM.
The experimental design tested for the effect of inshore versus deep water cable placement. Researchers found that few biological effects could be detected from patterns of species relative abundance, and there was no evidence of behavioral response by electro-sensitive species.
The experiment was undertaken in a natural setting using existing, undersea power cables connected from three drilling platforms in the Southern California OCS.
The researchers did not observe any significant differences in the fish communities living around energized and unenergized cables and natural habitats. Overall species diversity and the densities of the most important fish species, defined as comprising at least 1 percent of all fishes observed, were higher at the cables than at the natural habitats. This is likely due to the more complex habitats afforded by the cables than the primarily soft substrata natural habitats, according to the researchers.
Similar to the fish communities, the invertebrate assemblages living around energized and unenergized cables and natural habitats were similar to one another and the variability between these communities was driven primarily by sea floor depth.
The researchers also wanted to find out if electro-sensitive species such as sharks and rays respond, by either attraction or repulsion, to the EMFs of an in situ power transmission cable. They observed very few individuals of electro-sensitive species on the energized or unenergized cables or on the natural habitats. They found no compelling evidence that the EMF produced by the energized power cables in this study were either attracting or repelling fish or macro invertebrates.
The EMFs produced by the energized cables were similar both over the three years of the study and along the cables.