Estimating fish abundance at spawning aggregations from courtship sound levels

Timothy J Rowell,Octavio Aburto-Oropeza,John R Hyde,David A Demer,Brad E Erisman,Juan José Cota-Nieto

doi:10.1038/s41598-017-03383-8

Abstract

Sound produced by fish spawning aggregations (FSAs) permits the use of passive acoustic methods to identify the timing and location of spawning. However, difficulties in relating sound levels to abundance have impeded the use of passive acoustics to conduct quantitative assessments of biomass. Here we show that models of measured fish sound production versus independently measured fish density can be generated to estimate abundance and biomass from sound levels at FSAs. We compared sound levels produced by spawning Gulf Corvina (Cynoscion othonopterus) with simultaneous measurements of density from active acoustic surveys in the Colorado River Delta, Mexico. During the formation of FSAs, we estimated peak abundance at 1.53 to 1.55 million fish, which equated to a biomass of 2,133 to 2,145 metric tons. Sound levels ranged from 0.02 to 12,738 Pa2, with larger measurements observed on outgoing tides. The relationship between sound levels and densities was variable across the duration of surveys but stabilized during the peak spawning period after high tide to produce a linear relationship. Our results support the use of active acoustic methods to estimate density, abundance, and biomass of fish at FSAs; using appropriately scaled empirical relationships, sound levels can be used to infer these estimates.

Highlights

Quantitative assessments of fish abundance form the basis of fisheries management and conservation strategies[1, 2], but the complex migratory patterns, broad spatial distributions, life histories, and population dynamics of many fish species make it difficult to survey entire populations[3]
We developed active and passive acoustic methods to assess the abundance of Gulf Corvina (Cynoscion othonopterus; family Sciaenidae), hereafter Corvina, at its fish spawning aggregations (FSAs) and constructed a model to quantify relationships between sound levels and fish density during spawning
The results of this study demonstrate that sound levels may be used to estimate the densities of soniferous fishes at FSAs, which provides an alternative means to assess their abundance, biomass, and spatial distribution

Summary

Introduction

Quantitative assessments of fish abundance form the basis of fisheries management and conservation strategies[1, 2], but the complex migratory patterns, broad spatial distributions, life histories, and population dynamics of many fish species make it difficult to survey entire populations[3]. Some of these challenges are minimized if surveys are conducted where and when fish form large conspecific spawning aggregations[4]. Common Names Herrings, Shads, Sardines, Menhadens Cods and Haddocks Jacks and Pompanos Croakers, Drums, and Weakfishes Porgies Groupers and Sea Basses Snappers Rockfishes, Rockcods, and Thornyheads Goatfishes Grunts Cusk-eels Wrasses Catfishes Surgeonfishes, tangs, unicornfishes Parrotfishes Sturgeons Toadfishes

Methods

Results

Conclusion