Fish migration between a temperate reservoir and its main tributary

Abstract

Upstream- and downstream-directed migration between the Římov Reservoir and its only tributary, the Malše River (Czech Republic) was studied using two giant traps, sited at the mouth of the tributary, during the spring and summer periods, 2000–2002. The highest number of fish species was found in the tributary area (26 species and one hybrid). Over 10% of all fish biomass of the reservoir migrated through the tributary zone. The most important migration, in terms of fish numbers and intensity of movement, was the upstream spawning run. The fish species living in the reservoir can be divided into three groups: (1) the obligatory tributary-spawners (asp Aspius aspius(L.), bleak Alburnus alburnus (L.),chub Leuciscus cephalus(L.), and white bream Blicca bjoerkna(L.)); (2) generalists — fish spawning both in the tributary and the reservoir (bream Abramis brama(L.),roach Rutilus rutilus(L.), perch Perca fluviatilisL., pike Esox luciusL., and ruffe Gymnocephalus cernuus(L.)); and (3) fish spawning out of the tributary area (carp Cyprinus carpioL., pikeperch Stizostedion lucioperca(L.), catfish Silurus glanis L. and eel Anquilla anguilla(L.)). Tributary spawning is likely to support the strong roach population in the river upstream. Downstream migration from the river by salmonids appeared to be less important, in terms of relative numbers. Asp, roach and perch migrated as single spawners, bleak, bream and chub as multiple spawners. It was possible to define six periods of migration succession during spring and summer, which differed in species dominance, gonadal status and migration rates. The sequence starts with asp spawning and finishes after local movements of resident fish replace the spawning migrations. The most spectacular period during this sequence is the mass spawning of cyprinids when the roach, bleak, chub and bream migrate upstream and spawn nearly synchronically. During this period the daily migration rate exceeded 1000 individuals, which is over 100 times higher than during the feeding migration period.