Abstract:
Literature related to pool-type fishways has seen a recent
upsurge of interest in the placement of instream structures for
improving fish passage. However, there is still no information
on how different flow regimes created by boulder placement
have an influence on upstream fish movements. The main goal
of this study was to assess the performance of two different
flow regimes, characterized by the relative depth of flow (d/h),
where d is the water depth and h is the height of artificial bottom
substrata, in assisting fish passage in an experimental fullscale
pool-type fishway. Two series of experiments consisting
of 20 replicates each and representing distinct flow regimes
created by boulder placement in the flume bottom – d/h > 4
(regime 1) and 1.3 < d/h < 4 (regime 2) – were carried out to
analyse the proportion and timing of successful upstream
movements of a potamodromous cyprinid, the Iberian barbel
(Luciobarbus bocagei). Although no significant differences
(P > 0.05) in passage success were observed between regimes
(55% and 60%, respectively), fish transit time was significantly
lower (P < 0.05) in regime 2 (mean ± SD: 2.6 ± 1.6 min.) than
in regime 1 (7.1 ± 5.8 min.). The results of these experiments
show that lower relative depths can be more beneficial to fish
passage because they reduce the transit time for successful
negotiation, thus providing a useful indication on how to
improve fish passage through pool-type fishways.
