Impact of flow regulation for hydroelectric production in the movement patterns, growth and condition of a potamodromous fish species

Regulation for hydroelectric production (i.e., hydropeaking) can impact aquatic species life cycle. During 2016-2017, radiotelemetry was used to track 22 Iberian barbels during a 1-year cycle in a flow regulation scenario. Periodic samples of scales and biometric data were collected in a regulated (hydropeaking regime) and non-regulated river within the same basin for comparison. Collected tracking, growth and condition data were compared with similar information for the same barbel population, obtained exactly on the same river stretch in a pre-regulation period (2013-2014). Results on movement patterns of target species showed no effect of regulation on this biological component. However, potential intraspecific differences on migratory behaviour were found. We identified two behavioural profiles in each of the tagged fish groups: a 'resident' group that remains in upstream areas of the river during all the year round [maximum distance travel: mean (+/- SD) = 5.44 +/- 5.36 km] and a 'potamodromous' group that travels long distances downstream after the reproductive season (20.24 +/- 6.30 km). Flow regulation did not seem to affect the growth of the studied barbel populations; however, in terms of condition, differences between the pre- and post-regulation periods were detected, with this parameter being higher for juvenile fish during the post-regulation period. This study reveals important biological aspects of fish populations under short-term flow regulation for hydroelectric purposes that should be considered in future monitoring programmes, when dam construction is planned, in order to develop more specific measures to improve habitat availability and quality for fish.