Red rock crab (Cancer productus) movement is not influenced by electromagnetic fields produced by a submarine power transmission cable

Marine renewable energy (MRE) devices, such as ones that harness offshore wind and wave energy, are an effective supplement to traditional energy sources and can support the energy grid while combating climate change. As MRE development increases pace, it is important to anticipate impacts of these infrastructure projects on the marine environment. One potential impact is a localized change in electromagnetic fields (EMF) produced by energized submarine transmission cables. Though many marine species are sensitive to EMF, primarily for navigation and orientation purposes, strong conclusions about how EMF affects invertebrates are lacking. Organisms that traverse the seafloor close to energized submarine cables, such as crabs, may be subject to stronger EMF currents. The U.S. West Coast is both a hot spot for emerging MRE development as well as home to the largest crab fisheries in the nation, there is an obvious concern on the potential impact development will have on fisheries. Our primary objective was to verify the response of red rock crabs in the presence of energized cables similar to those associated with existing MRE installations while also controlling for environmental conditions. We quantified and mapped local magnetic fields near an energized cable, tested crab responses in cable and control areas using a two-choice experimental cage in situ and described and quantified variables that were most likely to affect crab responses, including water current direction/velocity and magnetic field strength. Our results were remarkably consistent with previous studies: 1) crabs showed no preference for crossing/not crossing the cable; 2) crabs preferred to travel to the west regardless of the presence/absence of an energized cable; 3) while crabs preferred to travel to the west even more frequently in the absence of an energized cable, cable crossing and travel direction preferences were not influenced by EMF; and 4) EMF produced by these cables were consistent over time and decay to background levels at a distance of less than 1 m. This information is critical to making informed and sustainable policy decisions about renewable energy development and ensuring that this technology can coexist with local fisheries as MRE development continues.