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Title: The Use of a Hydroacoustic Counter for Assessing Salmon Stocks
Author: Gregory J
Author: Environment Agency
Document Type: Monograph
Annotation: Environment Agency Project ID:EAPRJOUT_206, Representation ID: 26, Object ID: 1554
This R&D report assesses the performance of a split-beam echo sounder for enumerating the passage of migrating adult salmon. The equipment was manufactured by Hydroacoustic Technology Incorporated (HTI) and the three-year trial was conducted on the River Wye. Details of the background to the project are given along with basic acoustic theory plus the principles behind system operation. A protocol for site selection is listed using the Wye as an example. The results of the study show that Atlantic salmon present an acoustic target large enough to be detected above background noise levels typical of potential sites on many UK rivers. Fish targets were detected and enumerated as they passed through the beam over a range of environmental conditions. Like the alternative methods of salmonid enumeration, the successful application of this tool is dependant on aspects of site selection, riverine characteristics and fish behaviour. In addition, the ability to assess the proportion of fish passing through the ensoniiied area of the water column over a range of flows is required. The high debris load of the Wye caused several problems. The automatic “real time” fish tracking and counting facility of the system could not be solely relied upon to obtain robust data on fish passage. Multiple counting of single targets and spurious counts from downstream drifting weed caused the tracking software to over count. Every upstream target had to be verified manually after data collection. A method of validating the data produced by the acoustic counter using underwater video cameras was trialed. The results from this small scale operation suggested that the counter detected 80% of fish passage under trial conditions. A by-product of the project was the discovery that twaite shad (Alosa fallax) demonstrate a strong avoidance reaction to sound transmitted at 2OOkHz, well above the range previously reported for other Clupeid species. They were not repelled by sound transmitted at 42OkHz.
Publisher: Environment Agency
Subject Keywords: RiversSalmon fisheriesMigrationFish countersAcousticsFreshwater ecologyMarine environment
Geographic Keywords: British IslesWalesWye (Anglo-Welsh border)
Extent: 97
Total file downloads: 45

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