Soundscapes from a Saltwater Creek Captured by a Hydrophone Array

Abstract

Soundscape recordings allow listeners to know about the presence and activities of soniferous animals in an area, and these recordings have been used to learn about both terrestrial and aquatic environments. If we want to learn about animals that we cannot see, we can listen to them. But most soundscapes recorded with a single hydrophone provide little information about the locations and movements of the sound-producing animals in the recording because hydrophones are omnidirectional at low frequencies. Therefore, we deployed a seven-hydrophone array in a very shallow saltwater marsh to learn about the locations of sound producers and their movements. The study site was at the University of South Carolina Baruch Marine Field Laboratory in the North Inlet-Winyah Bay National Estuarine Research Reserve near Georgetown, SC, USA. We deployed the hydrophones in water of depths of 1.00 m to 1.70 m and recorded sounds using an eight-track simultaneous-sampling digital recorder for 24 hours. We determined the hydrophone positions by triangulating to known reference positions using a laser rangefinder and validated them using a Wide Area Augmentation System-enabled Global Positioning System (WAAS-GPS). We measured the time delays between the receivers by producing impulsive sounds underwater at known positions to calibrate the array. Although the array was deployed in a sub-optimal configuration, we were able to adjust the delays between the recordings to augment sounds produced at specific positions and identify the locations of sound sources. We detected sounds produced by Atlantic croaker Micropogonias undulatus, bighead searobin Prionotus tribulus, oyster toadfish Opsanus tau, silver perch Bairdiella chrysoura, spotted seatrout Cynoscion nebulosus, and striped blenny Chasmodes bosquianus as well as snapping shrimp (family Alpheidae). While many of the sound producers were stationary, we were able to track a spotted seatrout that was calling as it swam by the array. In this presentation we describe the soundscape and show positions and times for many of the soniferous animals we recorded.