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Title: Factors Affecting Coarse Fish Recruitment: Phase II - Examination and Analysis of Existing Environment Agency Data
Author: P A Frear
Author: I G Cowx
Author: Environment Agency
Document Type: Monograph
Annotation: Environment Agency Project ID:EAPRJOUT_1214, Representation ID: 599, Object ID: 2430
The aim of this project was to determine whether or not the data held by the Environment Agency are adequate to elucidate the main factors affecting coarse fish recruitment. This entailed primary analysis of the fisheries data and environmental information, such as water temperature, that are available within the Agency. In addition, the data were used to assess the most appropriate method of quantifying year class strength for subsequent analysis. Data on surveys of coarse fish populations and associated habitats were collected from all 26 Areas of the Agency and assessed for their utility in examining aspects of fish population dynamics, specifically relating to numbers of fish recruiting to the populations at the age of first spawning. Collation of the data sets provided an appreciation of the type, quantity and quality of coarse fish survey data gathered over a period of years in each Area, its accessibility, storage formats and locations. Many shortfalls in the data were found with respect to quality and quantity to support assessment of the factors affecting coarse fish recruitment in rivers. This was mainly because the data were not collected for the purpose of understanding these processes. All species displayed a period of good recruitment and stronger year classes during 1975-76, especially for roach and chub. A period of weaker year classes was observed during 1977-80 for all species except bream, the latter possibly because of errors in age determination. The analyses indicated that the strong roach and chub, and to a lesser extent bream and dace, year classes of 1975-76 have not been repeated in recent years and only roach appeared to be recruiting in a “consistently” cyclical pattern since this period. The relative strengths of the 1980-83 bream year classes are reflected in the relatively low YCS of many cohorts since this period, with 1987 and 1994 being the only two year classes that were prominent. Dace have not expressed a very strong year class since 1982 and may reflect considerable variation in YCS between rivers after this period. Chub also appear to exhibit a similar degree of variability in YCS between rivers in recent years, although ageing drift may account for some of this lack of complementarity.
Publisher: Environment Agency
Subject Keywords: Flow rateRoachTemperatureSurvivalChubRiversAge determinationMortalityBream
Taxonomic Keywords: Rutilus rutilusLeuciscus cephalusAbramis brama
Extent: 72
Total file downloads: 312

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