The mahseer fishes (Tor spp.) represent an iconic genus of large-bodied species of the Cyprinidae family. Across the 16 recognised species in the genus, individual fish can attain weights over 50 kg, resulting in some species being considered as premier sport fishes. Tor species also generally have high religious and cultural significance throughout South and Southeast Asia. Despite their economic and cultural importance, the status of Tor fishes has been increasingly imperilled through their riverine habitats being impacted by anthropogenic activities, such as hydropower dam construction and exploitation. Moreover, conservation efforts have been constrained by knowledge on the genus being heavily skewed

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Research into the relationships between non‐salmonid fish population dynamics and discharge is in its infancy compared with salmonids, thus compromising the ability to manage flows in rivers and maintain ecological status. This study reviews the potential role of ‘natural’ hydrographical variability on fish life‐history characteristics and develops a fish typology based on flow preference and conservation importance criteria that can be used to underpin the needs of hydrological management to support these fish community types. It highlights important characteristics of the natural flow regime that need to be maintained to ensure sustainability of populations of these species and offers a mechanism to categorise the fish community types, thus allowing generic management scenarios to be developed rather than complex single‐species scenarios that are impractical.

The exploitation of riverine systems for renewable energy has resulted in large numbers of small-scale hydropower schemes on low-head weirs. Although considered a clean and ‘green’ energy source in terms of emissions, hydropower can affect upstream migrating species by diverting flow away from viable routes over the impoundment and attract fish towards the turbine outfall. In an attempt to reduce this negative effect, hydropower outfalls with co-located fish-passage entrances are recommended, utilising turbine flows to attract fish towards the fish pass. The present study used acoustic telemetry to understand the performance of a co-located Larinier fish pass at a low-head hydropower scheme at a weir on the tidal Yorkshire Esk, England. The majority of the sea trout (anadromous Salmo trutta L.) individuals that approached the impediment were attracted to the hydropower and the co-located fish pass. Fish ascended through the pass under a wide range of river flows, tide heights, downstream river levels and hydropower flows, and there was no evidence that the hydropower operation affected fish-pass ascent. The information presented is urgently required to inform management decisions on the operation of hydropower schemes during the migratory period of salmonid fish, and help determine best-practice designs and operation at these facilities.

The hydrological regime is a significant driver of fish population dynamics in rivers, but there is a dearth of information regarding the mechanisms behind its effects on temperate species, especially non‐salmonids. This study investigated the effects of periodic and episodic flow pulses on 0+ fish biomass in a constrained lowland river. De‐seasonalized cross‐correlation analysis was used to examine time‐lagged correlations in episodic signals, in isolation of seasonal periodicity, to identify the responses and response timings of 0+ fish production to abiotic variables, and whether apparent “pulse‐depletions” in biomass occur instantaneously (e.g., due to fish displacement during high pulses) or after a time lag. As anticipated, 0+ fish biomass was highest during periods of low discharge and high temperatures in summer, but cross‐correlation analysis revealed a negative impact of high pulses on 0+ fish biomass with a lag of 7 months. There was no evidence for an instantaneous pulse‐depletion effect of discharge on 0+ fish biomass, suggesting that the indirect effects of high pulses, such as habitat or food‐web modifications, are more influential.