Sammendrag
Dams and turbines associated with hydroelectric power plants (HEP) disrupt connec-
tivity by affecting fish movement and survival. There has been an increasing focus on
measures to facilitate downstream migration at HEPs. The fish guidance efficacy
(FGE) of downstream mitigation measures largely remains suboptimal and calls for
development of knowledge on factors influencing FGE. In this study, we analyse
6 years of wild Atlantic salmon smolt passive integrated transponder (PIT)‐telemetry
data (N = 1,498) from a neighbouring small‐ and a large‐scale HEP. Timing of the
smolt migration period was significantly different between the two rivers. Thus, river‐
specific smolt‐run timing is imperative for proper measures management in regulated
rivers aiming at maximizing smolt‐descent survival. A generalized linear model including
additive effects of relative bypass discharge and scaled river discharge on the FGE
for descending smolts received highest Akaike's information criterion support in the
data and explained 74.2% of the FGE variation. This model, including no river effect,
predicted high FGE (up to 90%) at low river flow (≤30% of HEP maximum capacity)
when 7% of the water is allocated through the bypass. Many run‐of‐the‐river HEPs
have highly variable river flow during the smolt‐run period. Our model suggests that
these HEPs could utilize their manoeuvre flexibility to obtain water allocation routines
between bypass and turbines that optimize both FGE and hydroelectric production.
bypass, fish guidance efficiency, passive integrated transponders, run‐of‐the‐river, salmonids
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