Propagation loss of spawning calls produced by spotted seatrout Cynoscion nebulosus and the effective detection area of passive acoustic sampling

Abstract

Acoustic signaling in fish has been observed in conjunction with various behaviors but most commonly is associated with spawning. Sound production has been used to identify spawning sites for multiple species, but sound propagation characteristics are often not accounted for, severely limiting the spatial resolution at which spawning sites can be identified. We examined the propagation loss of seatrout calls in the very shallow environment of an estuary using recorded calls and an array of stationary hydrophones. We estimated the minimum expected source level of a seatrout call from the maximum recorded sound pressure level (SPL) of individual fish calls made in situ at spawning sites. Based on preliminary data from 86 samples, the minimum expected source level of an individual call is 142.1 ± 0.9 (CI₉₅) dB_rms re: 1 µPa at 1m. Measurements of propagation loss were fitted with a logarithmic model, and preliminary results showed that seatrout calls were detectable above background noise levels between 64 m and 512 m from the source. These results can be used to relate sound levels to the abundance of fish present at a spawning aggregation and enhance the precision of locating spawning sites using passive acoustics.