Fish pass assessment in the rivers of Catalonia (NE Iberian Peninsula). A case study of weirs associated with hydropower plants and gauging stations

Abstract

Fish pass assessment in the rivers of Catalonia (NE Iberian Peninsula). A case study of weirs associated with hydropower plants and gauging stations This study evaluated the effectiveness of fish passes in Catalan rivers (NE Iberian Peninsula). The aim was to test current functionality to enhance these structures for the purpose of optimising their management. We analysed river connectivity and fish pass facilities to generate information to improve the design, construction, management and assessment of solutions related to fish passage in Catalan rivers according to international best practices. In 2006, a preliminary evaluation of the locations and effectiveness of fish pass facilities in Catalonia was conducted through direct inspection of 78 fishways. Most of them were retro-fitted solutions using broad-spectrum technical structures, mainly pool fishway or pool pass facilities. An analysis of the effectiveness of 7 of the new fish passes (4, 2 and 1 passes in the Ter, Ebro and Tordera rivers, respectively) was performed between 2006 and 2009. The fish passes were located in weirs associated with hydropower plants and gauging stations. Our preliminary assessment of fish connectivity was based on a field visit and collection of information to populate a database of existing obstacles and associated fishways and calculation of the new version of the ICF index (river connectivity index) for all of them. Several methodologies were used to check the effectiveness of a selection of fish pass solutions, most of which were based on passage rates directly or indirectly estimated for each species. Direct estimation techniques involved the installation of fish traps upstream of the facility at the exit of the fish pass and visual counts. Indirect estimation techniques compared the fish population structure on each side of the obstacle in river sections with equivalent hydrology and habitat characteristics using electric fishing or trapping systems, group mark-recapture methods and individual mark-recapture methods (PIT tags). The results showed that (1) existing solutions to improve fish migration in Catalonia are insufficient (only present at approximately 8% of obstacles), and where they do exist, thefish passes are usually inadequate or poorly maintained. (2) Fish passes are generally inadequate or insufficient for the total native fish fauna from each water body. Additionally, with few exceptions, fish passage rates are too low, and in most cases, only fish with a high capacity to overcome obstacles or the largest individuals succeed in migrating. (3) Fish pass effectiveness agrees with the results of the new version of the ICF index.