Fish community structure in lowland drainage channels

Land drainage channels constitute a vast network of aquatic habitat utilized by fish. Surveys of these channels (dykes) in Broadland in eastern England reveal similar fish communities whether the dykes drain grazing marsh, fenland or arable land, though there are indications of poor recruitment in the recently deeply drained dykes of arable land. The species encountered most predictably were pike, roach, eel and tench. In terms of biomass, pike ranked top, followed by tench, bream and roach. Eels could not be sampled quantitatively but they must rank in the top five species in terms of biomass. Ordination and other analyses of community structure revealed several physicochemical and biotic factors that correlate with fish distribution and abundance. In particular, the presence of a floating plant mat in summer was associated with low oxygen concentrations at night and the absence of roach. The composition of fish communities in dykes contrasts in a number of ways with those recorded in local rivers and lakes (broads).