Resonance classification of mixed assemblages of fish with swimbladders using a modified commercial broadband acoustic echosounder at 1–6 kHz

Abstract

Recently developed broadband acoustic methods were used to study mixed assemblages of fish spanning a wide range of lengths and species. Through a combination of resonance classification and pulse-compression signal processing, which provides for high-range resolution, a modified commercial broadband echosounder was demonstrated to provide quantitative information on the spatial distribution of the individual size classes within an assemblage. In essence, this system spectrally resolves the different size classes of fish that are otherwise not resolved spatially. This method reveals new insights into biological processes, such as predator-prey interactions, that are not obtainable through the use of a conventional narrowband high-frequency echosounder or previous broadband systems. A recent study at sea with this system revealed aggregations containing bladdered fish 15-30 cm in length (Atlantic herring (Clupea harengus) and silver hake (Merluccius bilinearis)) and a variety of species of smaller fish 2-5 cm in length. These observations infer that the smaller 2-5 cm fish can be colocated in the same aggregations as their predator, the larger silver hake, as well as pre-spawning herring. While this technological advancement provides more information, there remain challenges in interpreting the echo spectra in terms of meaningful biological quantities such as size distribution and species composition.Résumé : Des méthodes acoustiques à large bande récemment mises au point nous servent à étudier des peuplements mixtes de poissons couvrant un large éventail de longueurs et d'espèces. Par une combinaison de classification des résonances et de traitement des signaux de compression des impulsions qui fournit un haut degré de résolution, un échosondeur commercial modifié à large bande s'avère capable de fournir des données quantitatives sur la répartition spatiale des classes d'âge individuelles au sein d'un peuplement. Spécifiquement, le système permet une résolution spectrale des différentes classes de taille des poissons qui autrement ne peuvent être distinguées dans l'espace. La méthode ouvre de nouvelles perspectives sur les processus biologiques, tels que les interactions prédateurs-proies, qu'on ne peut obtenir par l'emploi d'un échosondeur ordinaire de haute fréquence à bande étroite, ni par les systèmes à large bande plus anciens. Une étude récente en mer avec ce système montre des rassemblements de poissons à vessie natatoire de longueurs de 15 à 30 cm (harengs atlantiques (Clupea harengus) et merlus argentés (Merluccius bilinearis)), ainsi qu'une variété d'espèces de poissons plus petits de longueurs de 2-5 cm. Ces observations laissent croire que les poissons plus petits de 2-5 cm peuvent être localisés ensemble dans les mêmes rassemblements que leurs prédateurs, les merlus de plus grande taille et les harengs avant la fraie. Bien que cette avancée technologique fournisse plus d'information, il reste des défis pour interpréter les spectres des rétrodiffusions en regard de quantités biologiques sig...

Broadband classification and statistics of echoes from aggregations of fish measured by long-range, mid-frequency sonar

“…[17][18][19] For example, the gaseous swimbladder-bearing fish, observed in this experiment, produced a resonance in or near the frequency range of the employed sonar (1.5-5 kHz). Due to the strength of the resonance, the fish echoes could be observed above the background reverberation.…”

“…Additionally, this study is complemented by previous measurements taken in the same region using a downward-looking, broadband (1-6 kHz) system that largely overlaps with the frequency band used in this study. Those measurements, collected during a series of experiments, [17][18][19] provide empirical validation of swimbladder-resonance characteristics observed in this experiment.…”

“…A hull-mounted, downward-looking Simrad EK60 scientific echosounder collected multi-frequency (18,38,120 kHz) acoustic data continuously aboard the FRV Delaware II. These echosounder data were processed by the NEFSC team using a combination of manual analysis and automated classification and detection algorithms to identify schools of fish with gas-filled swimbladders, classify these aggregations into Atlantic herring (Clupea harengus) and non-herring schools, and extract parameters for each school (e.g., school depth, school length, school thickness, and volume backscattering strength).…”

A Review of the Tools Used for Marine Monitoring in the UK: Combining Historic and Contemporary Methods with Modeling and Socioeconomics to Fulfill Legislative Needs and Scientific Ambitions

“…A more recent development in commercial echo sounders, broadband, further utilizes this concept by chirping across a broader band width. Advantages include the combination of a controlled transmit signal, more suitable transmit repetition rate, and pulse-compression processing, resulting in much higher vertical resolution (Stanton et al, 2010(Stanton et al, , 2012.…”

Analysis and Classification of Broadband Acoustic Echoes from Individual Live Fish using the Pulse Compression Technique

“…, chirp (sonar) , , SNR (signal to nose ratio, ) , , (Airmar, 2013 Stanton, 1998). chirp (Stanton and Chu, 2008;Stanton et al, 2010;Stanton et al, 2012). , , .…”