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Title: Semi-Quantitative Methods for Fisheries Classification
Author: Wyatt Rj
Author: Environment Agency
Document Type: Monograph
Annotation: Environment Agency Project ID:EAPRJOUT_497, Representation ID: 165, Object ID: 1836
In recent years, the Agency has increasingly used low-cost “semi-quantitative” methods. for fish stock assessment in rivers in an attempt to make monitoring programmes more costeffective. However, semi-quantitative methods only produce a relative index of fish abundance and yet a number of monitoring objectives, including the Agency’s Fisheries Classification Scheme (FCS), require an absolute estimate of abundance. There is therefore an urgent need to develop nationally consistent calibration methodologies that will enable the results of semi-quantitative surveys to be used for fisheries classification purposes. This report discusses the various approaches to calibrating semi-quantitative methods, and critically assesses a number of Regional calibration exercises undertaken by the Agency and its predecessors. Three areas for improving these methodologies are identified: 1) a correction for different types of river habitat, 2) the assessment of classification errors and 3) a refinement of the statistical-procedures used. A new calibration methodology is developed in the report that addresses these three issues. A Bayesian approach is used estimate the Probability of Class for the FCS from semi- quantitative data. The rationale of the method is explained and illustrated for trout using a database of around 600 sites. Details of the statistical basis of the methodology are given in the appendices. The report concludes by recommending improvements to Agency operational practice in relation to semi-quantitative methods and further R&D needs. Recommendations for operational practice include the routine collation and archiving of data relating to method efficiency and the development of national calibration relationships for a range of species and associated implementation software. R&D needs include an objective assessment of the role of semi-quantitative methods in fisheries monitoring and further refinements to the calibration methodology. Finally, a methodology for estimating Probability of Class for quantitative methods does not currently exist, and it is recommended that quantitative methods are further developed to achieve consistency between quantitative and semi-quantitative approaches.
Publisher: Environment Agency
Subject Keywords: RiversRiver fisheriesStock assessmentFishery surveysPopulationFreshwater ecology
Extent: 59
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