It is likely that for the foreseeable future, offshore renewable energy technologies (e.g., wind and wave) will focus on the generation of electricity. These technologies harness energy from an array of individual devices and, through power cables, send electricity to shore via cables. These cables will transmit either alternating current or direct current, and, if the cable uses alternating current, this current will generate both electric and magnetic fields.
Research has shown that some cartilaginous and bony fishes, as well as at least some invertebrates, are sensitive to electromagnetic fields (EMF) and that these fields can alter the behavior of these organisms (Kalmin 1982, Formicki et al. 2004, Tanski et al. 2005). However, worldwide, very few studies have been conducted to document the effects of EMF on marine organisms in situ (Ohman et al. 2007). Only one survey on the Pacific Coast has examined, in the marine environment, the role that EMF emitted from a cable might play. That study, Barry et al. (2008), found that longnose skate (Raja rhina) appeared to have been attracted to an energized sea-bed cable. However, it should be noted that rather than comparing energized and unenergized cables, this survey compared organism densities along a sea bed before and after an energized cable was installed. Thus it was difficult to differentiate the effects of the EMF emanating from the cable from the effects of the cable structure itself.
Submarine transmission cables that power offshore oil platforms in the Pacific Region provide a unique opportunity to assess potential behavior and reaction of electromagnetic-sensitive species to industry activities. In particular, the chance occurrence of both energized and unenergized cables in a corridor on the seafloor within the Santa Ynez Unit Offshore Southern California Planning Area, allows for an experiment testing the effects of EMF on marine organisms. The identical cables stretch several miles from Platforms Heritage, Harmony, and Hondo (at depths to about 326 m) to Los Flores on the mainland. The cables run from the platforms toward the mainland to a sea floor depth of 10 m and from there are buried inshore. One unenergized cable runs from a platform to the border of federal and state waters at a bottom depth of about 150 m. All of these cables use the industry standards of the power cables that will be used for connecting devices (35 KV) within renewable energy installations. These cables were emplaced concurrently by the manufacturer. Thus, the cables form a natural experiment, allowing a comparison of an energized power cable with one that is unenergized to determine the potential impacts from electromagnetic fields while controlling for the habitat effect contributed by the cables themselves. The goal of this study was to more fully understand the potential effects of energized, seabed deployed, power cables on marine organisms.
Specific objectives of this study were to determine:
- The differences among fish and invertebrate communities associated with energized and unenergized cable habitat and those communities in soft seafloor habitats lacking cables.
- Whether electrosensitive species that are regionally important such as sharks and rays respond (via either attraction or repulsion) to the EMF’s of an in situ power transmission cable.
- The strength, spatial extent, and variability of EMF’s along both energized and unenergized cables.
- The potential effectiveness of the commonly proposed mitigation of cable burial. Knowledge gained from this study will be directly applicable to renewable energy projects not only in the Pacific OCS region, but to any OCS planning area.