A comparison of techniques for ranging close-proximity mulloway (Argyrosomus Japonicus) calls with a single hydrophone

Abstract

The accurate ranging of sounds produced by fish can provide valuable information on species ecology, and fish calls are being increasingly used to delineate and evaluate spawning grounds. In 2008, a single hydrophone was deployed on the riverbed of the Swan River, Western Australia, to assess the most effective technique for ranging mulloway (Argyrosomus japonicus) calls. During this experiment, the ranges of a calling mulloway were calculated using four techniques. These techniques involved comparing the characteristics of the direct and surface -reflected paths using: 1) arrival-time difference; 2) the pressure-amplitude ratios; 3) pulse sound-pressure-level ratios and; 4) a combination of techniques 1) and 2). Technique 1 proved the most consistent ranging technique, with accuracy limited by wave-motion-induced variation in water depth. However, a combination of the tested techniques is recommended when ranging fish.