Coarse fishway assessment to prioritize retrofitting efforts: A case study in the Duero River basin

Abstract

Restoring the longitudinal connectivity of rivers is one of the main objectives of environmental European directives and policies. Fish passes or fishways are one of the most common actions for its restoration. Despite the great number of fish passes constructed during the last two decades to comply with these policies, few of them have been assessed and their suitability for fish movements is unknown. There are different options to assess fish passes, but time and economic costs frequently limit their application. Coarse fishway assessment methods (CFAMs) are an easy, fast and economic alternative for this purpose. This study aims to display the potential of CFAMs to evaluate a large number of fishways, to show the actual status of fishways in an Iberian representative river basin, and to diagnose their suitability and problems. For this, the Spanish Duero River Authority promoted the assessment of 64 stepped fishways in the Duero River basin (Spain) using the AEPS methodology. The results were analyzed considering the four stages that a fish must overcome in a fishway (attraction, entry, passage and exit), the fishway type and the construction period. Among others, results show that 50% of the assessed fishways allow the free movement of fish. However, this percentage could have been greater applying an adequate monitoring program for the fishway design and construction. Furthermore, the diagnosis by stages of the AEPS methodology allowed to identify the attraction and passage as the most problematic stages and also helped to define specific retrofitting solutions for each fishway. The study concludes that the application of CFAM during fishway design, construction and first operation stages can increase their effectiveness and, thus, the number of fish passes that contribute to the restoration of the longitudinal connectivity of rivers.