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Title: Factors affecting the recruitment of riverine coarse fish: phase 3
Author: R. Musk
Author: R. Britton
Author: Environment Agency
Document Type: Monograph
Annotation: Environment Agency Project ID:EAPRJOUT_1225, Representation ID: 396, Object ID: 2440
The aim of Phase III of the ‘Factors affecting the recruitment of riverine coarse fish’ (FARRCoF) project was to identify: - the extent to which ageing drift adversely influenced the year class strength (YCS) outputs of the FARRCoF Phase II project data; - how such issues may be remedied in future studies; - a new method for dealing with ageing errors and assessing YCSs - why and how the FARRCoF project should proceed to the next phase. In Phase II of FARRCoF, ageing drift was identified as an issue that affected the calculation of YCSs as indices of recruitment, by causing apparent changes in relative YCSs between survey samples. Examples were found of characteristically strong year classes moving to both earlier and later years, as well as oscillating between surveys. It was suggested that this might have been caused by errors in the ageing of these fish, which then produced an erroneous YCS output. The re-ageing of approximately 1200 scales from roach, dace and chub from the River Stour in Essex suggested that errors had indeed occurred in the original age determinations. These errors arose from the subjective interpretation of certain scale features, such as indistinct checks, and the growth season to which growth at the edge of the scale was ascribed. It was concluded that, without independent validation, such issues can never be eliminated from scale ageing and that their influence on existing YCS calculations was undesirable. As a result, it was recommended that new methods of assessing recruitment strength should be devised that can incorporate the subjectivity of scale ageing. Gap analysis was used to identify those aspects of the Environment Agency’s understanding of recruitment that remain incomplete. This highlighted the following gaps in knowledge. - Aspects of 0-group fish biology that determine the subsequent recruitment strength of cohorts; - The key abiotic and biotic factors in the early life history of cohorts that impact upon subsequent recruitment success; - The reproductive and life history traits that determine egg and larvae production, survival and subsequent recruitment; -The roles of habitat, discharge and flood plain management in regulating the carrying capacity of the fish stock, both in juvenile and adult life phases. It is recommended that these gaps in knowledge should be filled in future phases of the FARRCoF project. A number of discrete projects are proposed to assist in this process.
Publisher: Environment Agency
Subject Keywords: HabitatsCoarse fishesJuvenilesModellingAge determinationPopulation dynamicsStatistical dataParasitism
Geographic Keywords: EnglandWales
Taxonomic Keywords: Leuciscus leuciscusRutilus rutilusLeuciscus cephalus
Extent: 56
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