The influence of bottom rugosity on the performance of upstream fish movements through a pool-type fishway under different discharges

Paulo Branco, José Maria Santos, Christos Katopodis, Maria Teresa Ferreira, António Pinheiro

Tuesday 30 june 2015

16:00 - 16:15h at Amazon (level 1)

Themes: (T) Hydro-environment, (ST) Ecohydraulics and ecohydrology

Parallel session: 7G. Environment - Ecosystem

The placement of artificial substrates at the bottom of conventional fishways has been of increasing interest, as a means to improve passage for several fish species. The aim of this work is to study the behaviour and performance of the Iberian barbel (Luciobarbus bocage), a large benthic potamodromous fish, in a full-scale experimental pool-type fishway featuring different bottom substrates to test the effect of both macro-rugosity and roughness. For this purpose, two boulder arrangements (macro-rugosity) set at distinct densities (8 boulders/pool and 12 boulder/pool) and an artificial grass layout (roughness) were tested with two fishway discharges (Qlow = 38.5 L.s-1 and Qhigh = 62.7 L.s-1). Fish were collected in the field by electrofishing and transported to the laboratory, where they were held under adequate housing, nutrition and care conditions. When using macro-rugosities, fish responded with greater success (45% of successful passes) at the higher discharge, independent of boulder density. This was possibly due to the fact that upstream attraction was always guaranteed, something that did not happen in the lower discharge with a higher boulder density configuration (25% of successful passes). On the other hand, when facing a roughness grass layout (increased friction), fish responded with greater success at the lower fishway discharge (50% of successful passes) than at the higher discharge (30% of successful passes), where the presence of higher bottom velocities prevented further passage success. These findings show that placing macro-rugosity or roughness (case-specific) at the bottom of conventional fishways may facilitate passage, if an adequate fishway discharge is provided.