Towards a life‐history‐based management framework for the effects of flow on juvenile salmonids in streams and rivers

Abstract

Salmonid fishes have complex life cycles involving major changes in habitat requirements at different stages in their life history. Effects of changes in flow and flow regime on salmonids are therefore highly stage‐specific. Successful management requires consideration of stage‐specific influences and integration of these effects over the entire life history to predict ultimate impacts on abundance and population viability. The state of science regarding stage‐specific influences of flow regime on juvenile salmonids and their habitats, referring specifically to fundamental attributes of natural regimes and to characteristic alterations of these regimes associated with water management, is reviewed. It appears that a key consideration in integrating the stage‐specific impacts of flow is the extent to which flow‐related losses or gains early in ontogeny can be compensated by increased growth or survival later in juvenile life history. Further, fundamental interactions between flow and water temperature must be incorporated into the robust models ultimately required for science‐based management. In the absence of such models and data, the current state of science may be sufficient to target specific aspects of flow regimes that are critical to multiple life‐history stages, which can then serve as a basis for interim flow prescriptions and subsequent adaptive management.

Run-of-River hydropower and salmonids: potential effects and perspective on future research

“…These periods of accentuated low flow in spring and summer also correspond to important times for spawning, incubating, or rearing salmonids ( Table 2). As found by studies conducted in reservoir-storage systems and in unregulated rivers, increased temperatures coinciding with low flows have the potential to change the timing of spawning migrations and interspecific interactions (e.g., Freeman et al 2001;Bendall et al 2012;Malcolm et al 2012), reduce survival of smolts before and during migrations (Nislow and Armstrong 2012), and make fish more vulnerable to pathogens (Crozier et al 2008;Mantua et al 2010). Additionally, these extended periods of low flow can reduce water quality, limit movement of nutrients and sediment, and increase competition and predation (Lake 2000;Bradford and Heinonen 2008;Walters and Post 2011).…”

“…Although evidence in the peer-reviewed literature specific to RoR hydropower is more limited (n = 31), it suggests that water quality, habitat quantity, and geomorphology can also be affected by RoR hydropower operations (Kubečka et al 1997;Baker et al 2011;Nislow and Armstrong 2012;Bilotta et al 2016). Changes to NFR following diversion of flow can affect water quality mainly through changes to temperature regimes, pH, and dissolved oxygen (Valero 2012).…”

“…Anthropogenically created lower flows can also reduce the metabolic costs of foraging and maintaining position for fish, thus increasing the amount of energy available for growth, as has been shown in reaches downstream of large reservoir-storage hydropower systems (Cleary et al 2012). However, other research conducted in reservoir-storage systems supports the idea that reduced habitat availability due to lower flows downstream of reservoir-storage dams results in short-term increases in fish densities, subsequently leading to increases in competition among and within salmonid life stages and increased susceptibility to disease (Bradford 1994;Nislow and Armstrong 2012). Geomorphically, lower flows can also reduce the frequency, diversity, and quantity of microhabitats including gravel bars, side channels, and pools that are important for salmonid spawning, overwintering, and rearing as well as for refugia during extreme flow events like floods or droughts (Sedell et al 1990;Bonneau and Scarnecchia 1998;Walters and Post 2008).…”

“…These frequent fluctuations in flow caused declines of brown trout density (−50%) and biomass (−43%), displacement of 0+ trout, and no change to macroinvertebrates in the first year following flow diversion (Almodüvar and Nicola 1999). In reservoir-storage systems, rapid increases in flow have also been associated with the downstream displacement of juvenile trout, increased energetic costs for fry, and scouring of redds (Harby and Halleraker 2001;Nislow and Armstrong 2012). Conversely, rapid decreases in flow can lead to a decrease in stage in downstream reaches that can strand fish on rapidly dewatered channel margins or trap fish in disconnected side channels and isolated pools.…”

Daytime habitat selection for juvenile parr brown trout (Salmo trutta) in small lowland streams

“…However, most knowledge on brown trout physical habitat requirements is from studies in larger streams and rivers (Heggenes, 1988a;Heggenes et al, 1999;Armstrong et al, 2003;Parasiewicz and Dunbar, 2001). There is little knowledge on physical habitat requirements in small lowland streams that can be used to evaluate the effects of different water management actions such as water abstraction or stream restoration activities aimed at increasing stream flow and improving physical habitat conditions Conallin et al, 2010a;Nislow and Armstrong, 2012). Four habitat variables are known to affect the habitat selection of salmonids and carrying capacity in streams (Vezza et al, 2012); water depth (Kennedy and Strange, 1982;Heggenes, 1988aHeggenes, , 2002, water velocity (Heggenes and Traaen, 1988;Heggenes et al, 1999;Heggenes and Dokk, 2001), bed substrate (Heggenes, 1988b;Knapp and Preisler, 1999;Kondolf, 2000), and cover (Hubert et al, 1994;Bovee et al, 1998).…”