A diverse group of echogenic particles observed with a broadband, high frequency echosounder

Christian Briseño-Avena,Jules S Jaffe,Paul L D Roberts,Peter J S Franks,Howard Browman

doi:10.1093/icesjms/fsx171

Abstract

Abstract In 1980, Holliday and Pieper stated: “Most sound scattering in the ocean volume can be traced to a biotic origin.” However, most of the bioacoustics research in the past three decades has focused on only a few groups of organisms. Targets such as small gelatinous organisms, marine snow, and phytoplankton, e.g. have been generally to be considered relatively transparent to acoustic waves due to their sizes and relatively low sound speed and density contrasts relative to seawater. However, using a broadband system (ZOOPS-O2) we found that these targets contributed significantly to acoustic returns in the 1.5–2.5 MHz frequency range. Given that phytoplankton and marine snow layers are ubiquitous features of coastal regions; this works suggests that they should be considered as potential sources of backscatter in biological acoustic surveys.

Highlights

There is a continued interest in understanding the sources of oceanic backscatter and the use of echosounders to estimate the abundances and distributions of marine organisms
It is likely that other body properties have a stronger influence than size on the acoustic reflectivity of the organisms and marine snow studied in this work
In this work we have shown that individual gelatinous zooplankton and marine snow targets are capable of reflecting broadband, ultra high-frequency (1.5–2.5 MHz) acoustic energy

Summary

Introduction

There is a continued interest in understanding the sources of oceanic backscatter and the use of echosounders to estimate the abundances and distributions of marine organisms. Using acoustic methods to understand the distributions of biological acoustic scatterers in the water column requires knowledge of the acoustic properties of the targets. Several ground-truthing experiments (i.e. inter-method comparisons) and models have concentrated on understanding of the acoustic properties and detection of fishes, e.g. relatively little effort has been focused on planktonic organisms. Data from the latest generation of broadband sonars present new opportunities for acoustical investigations of plankton (Lavery et al, 2010; Trenkel et al, 2016). Such investigations require a thorough understanding of the capabilities and limitations of such systems

Methods

Results

Conclusion