Playback of acoustic thermometry of ocean climate (ATOC) -like signal to bony fishes to evaluate phonotaxis

Abstract

The aim of this study was to evaluate whether acoustic thermometry of ocean climate (ATOC) signals have a positive or negative phonotactic effect on the behavior of fish present near the sound source at Pioneer Seamount off Central California. We played back an ATOC-like signal to three species of rockfish kept within a 15×2-m field enclosure in Bodega Bay, California. Each subject was observed during a 25-min “silent” control period followed immediately by a test period comprised of a 5-min “ramp-up,” in which the sound level increased gradually to a peak level, and a 20-min period at constant peak level. The amount of time that each subject spent in 15 zones, each 1 m wide, at increasing distances from the sound transducer, was observed. It was suspended in midwater at the center of zone 1, the deepest portion of the enclosure. We observed little movement by fish in response to the playback of the ATOC signal. The subjects remained in zones 1 and 2, despite sound pressure levels present of 145.1–153.0 dB re: 1 μPa. Little difference existed in the behavior of fish during sound playback period and the “silent” control period. The median time interval that fishes occupied zone 1 was 100% of the experiment duration for both test and control periods (i.e., 6 of 11 subjects in the former remained exclusively within that zone versus 7 of 11 subjects in the latter).