Abstract
To help achieve effective longitudinal river connectivity, evaluation of the efficacy of fishway use by upstream-migrating fishes is needed. Larinier super active baffle (SAB) fishways are relatively cheap retrofit fish passes, suitable for low-head barriers, widespread in Europe and the most commonly fitted technical pass in Britain. Their suitability for non-salmonids, however, is poorly quantified. The efficacy of a 15% gradient SAB fishway and effects of flow regime and water temperature were tested for European river lamprey (Lampetra fluviatilis) using passive integrated transponder (PIT) and acoustic telemetry at a Crump weir on the River Derwent, Northeast England. In migration season 2013–14, over a wide range of flows, 90.1% of 350 tagged lamprey entered the fishway. One fish (0.3%) of those that entered the pass ascended successfully, even though measured water velocity was within laboratory-measured performance conditions for this species. Of 29 acoustic-tagged lamprey that visited the weir over the same period, four (13.8%) ascended it directly, during elevated flows. These data suggest that high turbulence and/or the physical characteristics of baffles may inhibit lamprey ascent of the pass. In migration season 2014–15, we tested the effect of adding studded modular plastic tiles adjacent to the fishway wall, employing PIT antennas separately interrogating the entrance and exit of each of the main fishway and tile routes. 85.8% (169) of 197 tagged lamprey entered the fishway, of which 72/169 (42.6%) entered the tile entrance. Passage efficiency of entrants was 7.1% (12/169), all of which used the tiled route. Reduced local flow velocity in combination with increased availability of resting habitat within the tiles may have facilitated increased passage. Although fishway passage efficiency increased after placement of the modular tiles, it remained half that measured for direct weir passage, both of which are inadequate for connectivity restoration. Quantitative tests of studded tiles placed on the sloping downstream weir face by comparison to control conditions may be more effective and are needed. This study demonstrates the importance of carrying out full-scale field tests to supplement possible solutions developed under laboratory conditions.
Highlights
Ca. 45 000 large dams, exceeding 15 m, were built during the 20th century (World Commission on Dams, 2000)
Attraction to the entrance is influenced by the amount and velocity of flow leaving the fish pass, but is dependent on migratory behaviour and swimming capabilities of fish species, while passage is reliant on hydraulic conditions such as flow velocity and shear stress and swimming ability (Kemp, 2012; Williams et al, 2012)
315 out of 350 lamprey released below Buttercrambe weir were detected at the entrance of the Larinier fish pass in MS1, only one (0.3%) successfully ascended it during the period 31 October 2013 to 26 February 2014 (119 days) (Table 1)
Summary
Ca. 45 000 large dams, exceeding 15 m, were built during the 20th century (World Commission on Dams, 2000). Fish passes often perform poorly for other taxonomic groups (Bunt et al, 2012; Cooke et al, 2005; Lucas et al, 1999, 2000; Noonan et al, 2012) Hydraulic conditions, such as flow velocity and turbulence, are critical to the performance of fish passes, both within the pass and at the tailrace (Larinier et al, 2002). If passage of a broad range of fish species is to be facilitated, consideration of different swimming modes, swimming capabilities (Noonan et al, 2012), behaviour (Kemp, 2012) and life history stages (Baras and Lucas, 2001) are essential criteria
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