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Empirical evidence suggests that marine animals perceive and orient to local distortions in the earth's natural magnetic field. Magnetic fields (MFs) generated by electrified underwater cables may produce similar local distortions in the earth's main field. Concern exists that these distortions may impact migration movements of MF-sensitive animals. The Trans Bay Cable (TBC) is a ± 200-kV, 400-megawatt, 85-km high-voltage direct current transmission line buried through San Francisco Bay (37° 56′ 8.81″ N, 122° 27′ 0.19″ W). Detections of adult green sturgeon implanted with acoustic transmitters were used from six cross-bay receiver arrays from 2006 to 2015 to investigate how inbound and outbound migration movements through lower portions of their route to/from upstream breeding grounds are related to the TBC's energization status (off/on) and other local environmental variables. Here, we assess how these variables impacted transit success, misdirection from the migration route, transit times, and migration path locations within stretches between the Bay's mouth and the start of the Sacramento River. Overall, there was varied evidence for any effect on migration behavior associated with cable status (off/on). A higher percentage of inbound fish successfully transited after the cable was energized, but this effect was nonsignificant in models including temperature. Outbound fish took longer to transit after cable energization. Inbound and outbound migration path locations were not significantly influenced by cable energization, but results suggest a potential subtle relationship between energization and both inbound and outbound paths. Overall, additional migration-based studies are needed to investigate the impact of anthropogenic cables on marine species. [ABSTRACT FROM AUTHOR]

Acoustic telemetry allows collection of data on the movement and survival of fish and other aquatic organisms. The passive form of this technology uses transmitters (tags) and fixed receivers to record when an organism is present at a given location. Understanding and interpretation of these data depends on knowledge of the detection range and detection probability of the receivers. This study examines factors affecting performance of tags and receivers designed for the Juvenile Salmon Acoustic Telemetry System (JSATS) at a location in the Sacramento River in CA, USA. A group of tags (n = 13) of two power output levels, each transmitting a unique code at five second intervals, were manually moved past a set of two fixed receivers in upstream and downstream directions along transects of different distances from the receivers at two different speeds. The factors that significantly affected detection probability were tag orientation and tag movement direction. Tag orientation had the largest effect on detection probability, with higher detection rates when the tag's piezoelectric transducer was directed towards the receiver. Detection probability (proportion of transmissions detected) was 30–50% out to 160 m. Detection efficiency (proportion of tags regarded as present) was 99–100% when tags passed within 25 m and 84–96% within 135 m of a receiver. These results have implications for the design and interpretation of acoustic tracking studies and the orientation of transmitters when implanted into fish. [ABSTRACT FROM AUTHOR]