Searching for the FishOASIS: Using passive acoustics and optical imaging to identify a chorusing species of fish

Abstract

Marine protected areas have been established off the California coast to ensure the persistence and resiliency of the marine ecosystems found here. Kelp forest habitats, in particular, support a diverse assemblage of fishes, many of which produce sound. From May to September 2017, a low-frequency (325–545 Hz) chorus was recorded near the kelp forests off La Jolla, California. The chorus begins each day approximately a half-hour before sunset and lasts for about 3–4 hours. During these times, spectral levels around 400 Hz increased by approximately 30 dB over, although there is significant day-to-day variability in received level. To identify the chorusing fish species, a Fish Optical and passive Acoustic Sensor Identification System (FishOASIS) was developed, consisting of a four-channel SoundTrap ST4300 acoustic recorder and four Sony α7s II cameras. Frequency-domain beamforming was used on signals recorded by the four-element, 20-m aperture, tetrahedral-shaped array to estimate the location of the fish chorus, which appears to be fairly fixed over time. The chorus also was used as a source of opportunity to measure transmission loss in order to determine whether kelp forests can act as acoustic refuges by sufficiently attenuating chorusing sounds. [Research supported by California Sea Grant and NSERC Postgraduate Scholarship-Doctoral.]