RIPARIAN ECOTONES AND SPATIAL VARIATION OF FISH ASSEMBLAGES IN PORTUGUESE LOWLAND STREAMS

The first results of a long-term study on the role of riparian ecotone s on the population and community dynamics of Iberian stream fish are presented and discussed. Riparian and macrophyte cover, bank slope and depth were among the most important variables affecting fish distribu tion. In general small fish favoured shallow areas with high macrophyt e cover, whereas large fish dominated in deep areas with a high ripari an cover. Slight spatial changes in terrestrial prey use were found su ggesting a minor role for this resource during autumn. Finally, no sig nificant spatial differences were found for linear growth, although so me differences were obtained for the condition factor.