Impacts of ecosystem-friendly drainage channel alterations on fish fauna and habitat in agricultural streams

Abstract

This study evaluated the impacts on fish fauna and habitat in streams supplying water for agriculture, caused by drainage channel alterations done with consideration of the ecosystem, in June 2002. Study sites, in Iwate Prefecture, Japan, included earthen channels downstream, earthen channels upstream, semi-encased channels (with concrete encasement on both sides), and encased channel sections. The investigation clarified the relationships between fish communities and environmental factors. Hydraulic conditions were important for conservation of fish fauna, and the condition of the substrate was important for several kinds of benthic fish. Total populations and the species of fish tended to be remarkably few in the encased channel sections compared with other sections. On the other hand, no significant difference was found in total population numbers and the species of fish in the semi-encased channel sections compared with earthen channel sections, and the earthen substrate was effective for the conservation of fish fauna to some degree in the semi-encased channel section. However, the study suggested that an earth substrate alone would be insufficient in the conservation of some benthic fish.