The use of acoustic cameras in shallow waters: new hydroacoustic tools for monitoring migratory fish population. A review of DIDSON technology

Abstract

European Union legislation, through the Water Framework Directive (2000/60/ EC), as well as national legislation, such as the 'Grenelle Environnement ' (2007) in France, requires restoration of ecological connectivity in streams to improve free circulation of migratory fish. Different methods (e.g. capture by trap or net, telemetry, hydroacoustics) are used to evaluate the efficiency of fish passes to estimate the migratory species abundance and analyse changes in their within-river distributions. Among these methods, hydroacoustics is non-intrusive, allowing long-term observation and description of fish populations based on physical properties of sound in water. However, the main limit to hydroacoustic tools is their difficulty in identifying species. Initially designed for military purposes, dual-frequency identification sonar (DIDSON) has been used in environmental management for a decade. This acoustic camera uses higher frequencies and more sub-beams than common hydroacoustic tools, which improves image resolution and then enables observation of fish morphology and swimming behaviour. The ability to subtract static echoes from echograms and directly measure fish length improve the species-identification process. However, some limits have been identified, such as automatic dataset recording and the low range of the detection beam, which decreases accuracy, but efficient tools are now being developed to improve the accuracy of data recording (morphology, species identification, direction and speed). The new technological properties of acoustic cameras, such as the video-like visualization of the data, have greatly improved monitoring of diadromous fish populations (abundance, distribution and behaviour), helping river and fisheries managers and researchers in making decisions.

Manual fish length measurement accuracy for adult river fish using an acoustic camera (DIDSON)

“…Its wide field of view (29 horizontally, 14 vertically) combined with a high number of beams (96 beams in highfrequency mode and 48 in low-frequency mode) provides a unique fish tracking efficiency. Furthermore, by allowing direct visualisation of fish morphology (more particularly length) and behaviour (Baumgartner et al, 2006), the acoustic camera offers clues for species identification (Martignac et al, 2015). In addition, it enables length measurements to be made directly from the images, thus avoiding bias on the conversion from target strength (TS) to metric units as done in fisheries acoustic using lower frequency (Rudstam et al, 2012).…”

Assessment of River Herring Spawning Runs in a Chesapeake Bay Coastal Plain Stream using Imaging Sonar

“…Electronic fish counters and video recordings have been used in other regions to conduct nearcontinuous river herring run counts, but these methods can impede fish in the spawning run due to the need for narrow fish passage structures, can be biased low in the case of electronic counters, and are less effective in turbid streams or at night in the case of video recordings (Hiebert et al 2000;Sheppard and Bednarski 2015). Imaging sonar has proven to be a powerful tool for conducting run counts for stock assessment in shallow streams several meters or less in depth and, importantly, can be used in turbid streams without narrow fish passage structures (Holmes et al 2006;Martignac et al 2014). Although river herring are small (200-350 mm TL) and thus challenging to image using sonar (Hightower et al 2013), imaging sonar has been used to conduct run counts for a variety of species groups including river herring (Magowan et al 2012) and salmonids Mueller et al 2010;Pipal et al 2010;Jones and Petreman 2015) and multispecies assemblages that include river herring (Grote et al 2014;Hughes and Hightower 2015).…”

Acoustic Target Strength of the Endangered Chinese Sturgeon (Acipenser sinensis) by Ex Situ Measurements and Theoretical Calculations

“…In addition, new and high-end acoustic technologies [39], such as wideband and multibeam echosounders as well as omni-directional sonars and imaging sonars, all could be combined to obtain a comprehensive understanding on the fish. To improve the survey efficiency, the multibeam echosounders with large detection range could be firstly used in the 1700 km middle and lower reaches of Yangtze River to ascertain the potential distribution areas of Chinese sturgeon, then the wideband echosounder and imaging sonars/acoustic cameras [40,41] could be used to conduct more intensive surveys in these areas.…”