Behavioral responses by migrating juvenile salmonids to a subsea high-voltage DC power cable

Currently, there is large-scale interest in developing marine-based energy sources and extensive subsea power cable networks. Despite growing concern that local perturbations in the magnetic field produced by current passing through these cables may negatively affect electromagnetically sensitive marine species, e.g., disrupted migration; few studies have examined free-living animals. We used acoustic biotelemetry tracking data to examine movement behaviors and migration success of a magneto-sensitive fish, late-fall run Chinook (LFC) salmon (Oncorhynchus tshawytscha), in relation to the energization of a magnetic field-producing subsea power cable, as well as other potentially influential environmental parameters. We analyzed detection records of tagged LFC salmon smolts during their out-migration through the San Francisco Bay before and after the installation of an 85-km high-voltage direct-current transmission cable. Cable energization did not significantly impact the proportion of fish that successfully migrated through the bay or the probability of successful migration. However, after cable energization, higher proportions of fish crossed the cable location and fish were more likely to be detected south of their normal migration route. Transit times through some regions were reduced during cable activity, but other environmental factors were more influential. Resource selection models indicated that proximity to the active cable varied by location: migration paths moved closer to the cable at some locations, but further away at others. Overall, cable activity appeared to have mixed, but limited effects on movements and migration success of smolts. Additional studies are recommended to further investigate impacts of subsea cables on fish migrations, including potential long-term consequences.