Observing individual fish behavior in fish aggregations: Tracking in dense fish aggregations using a split-beam echosounder

Abstract

Acoustic instruments are important tools for observing the behavior of aquatic organisms. This paper presents a simple but efficient method for improving the tracking of closely spaced targets using a split-beam echosounder. The traditional method has been a stepwise approach from the detection of echoes, rejection of apparently multiple targets and then tracking the remainder. This is inefficient because the split-beam angles are not included in the initial detection; rather they are only used in the rejection criteria before the subsequent tracking. A simple track-before-detection method is presented, where the phase angles, echo intensities, ranges, and times are used simultaneously, resulting in better detection and tracking of the individual fish. Two test data sets were analyzed to determine the effectiveness of this method at discriminating individual tracks from within dense fish aggregations. The first data set was collected by lowering a split-beam transducer into a herring layer. The second data set, also collected with a split-beam transducer, was from a caged aggregation of feeding herring larvae. Results indicate the potential of target tracking, using a split-beam echosounder, as a tool for understanding interindividual behavior.

Nighttime Swimming Behavior of a Mesopelagic Fish

“…High population densities hamper individual tracking detection (Handegard, 2007). Correspondingly, individuals close to the transducer are tracked more effectively due to the higher resolution of targets.…”

Target-tracking in a parametric sonar beam, with applications to calibration

“…The value of split-beam data is well appreciated from numerous target-tracking studies [19][20][21].…”

NEIGHBOUR-IN: Image processing software for spatial analysis of animal grouping

“…In order to study aggregation patterns, researchers can use various methods for data collection that could be divided into three mains categories (1) manual : observation and capture ( Krause et al 2000 ; Spieler 2003 ), photography and film ( Aschwanden et al 2008 ; Ballerini et al 2008 ; Boulay et al 2013 ; Eklund and Jensen 2011 ; Le Goff et al 2009 ; Yoshida et al 2010 ) (2) semi-manual : sonar and echo sound ( Axelsen et al 2001 ; Gerlotto et al 2006 ; Gerlotto and Paramo 2003 ; Handegard 2007 ; Soria et al 2003 ), (3) automatic : microtransponders ( Jeanson 2012 ), RFID tagging ( Planas-Sitja et al 2015 ).…”