Effect of regulation on 0+ fish recruitment in the great ouse, a lowland river

Abstract

AbstractThe recruitment of 0+ fishes in the River Great Ouse, East Anglia (U.K.), was investigated using electrofishing by Point Abundance Sampling, in order to compare the distribution and extent of fish reproduction in the river and its annexes (side channels, backwaters, etc.) with similar but unregulated lowland rivers of Europe. In all, 44 sites were sampled during three weeks in August 1989. Correspondence Analysis of the Sites‐by‐Species matrix (44 × 17) in density (fishes per m2) revealed a slight but notable longitudinal zonation of fish reproduction, unusual for lowland rivers, with the limnophils Blicca bjoerkna (L.), Scardinus erythrophthalmus (L.) and Abramis brama (L.) limited to lentic downstream sites and the rheophil Barbus barbus (L.) restricted to a few upstream sites. Thus, compared with unregulated rivers of Europe, the River Great Ouse differs by: (1) the absence of pelagic spawners, e.g. Lota lota (L.), which were historically reported as abundant; (2) the reduced range and abundance of both rheophilic and limnophilic cyprinids, e.g. B. barbus (L.), Alburnus alburnus (L.) and Blicca bjoerkna (L.), Scardinus erythrophthalmus (L.), Abramis brama (L.), Tinca tinca (L.); and (3) the predominance of generalists throughout the system, Rutilus rutilus (L.) downstream and Phoxinus phoxinus (L.) with Gasterosteus aculeatus (L.) upstream, probably to the additional detriment of the localized specialists, both limnophilic and rheophilic.