Responses of intermittent stream fish assemblages to irrigation development

Abstract

Large-scale irrigation projects are being undertaken in the Mediterranean region, and agricultural practices are being intensified, but their impacts on instream biota remain poorly documented. The present study assesses the effects of an irrigation scheme on fish community structure in Mediterranean streams. Fish assemblages were sampled in unregulated intermittent streams over 6years concurrently with the development of a new irrigation project in southwestern Iberia, and the biotic variation was separately related to increases in human activity and environmental gradients. Overall, fish assemblages were influenced by reservoir proximity (likely functioning as a source of non-native species), the proportion of irrigated lands, average water depth and wetted width (likely related with habitat permanency), and elevation. Results indicated that human actions linked to the irrigation project significantly shaped fish assemblage changes, after accounting for the effect of environmental variables. The proportion of irrigated lands in the catchment was related to some fish metrics (proportion of less tolerant specimens, proportion of invertivores and proportion of non-native specimens, except G. holbrooki). Our results support the thesis that the development and exploitation of irrigation schemes impact fish assemblages and reinforce the need to ensure that the ongoing agricultural intensification is compatible with the ecological integrity of Mediterranean intermittent streams.