Dam Operations Affect Route-specific Passage and Survival of Juvenile Chinook Salmon at a Main-stem Diversion dam

Abstract

Diversion dams can negatively affect emigrating juvenile salmon populations because fish must pass through the impounded river created by the dam, negotiate a passage route at the dam and then emigrate through a riverine reach that has been affected by reduced river discharge. To quantify the effects of a main-stem diversion dam on juvenile Chinook salmon in the Yakima River, Washington, USA, we used radio telemetry to understand how dam operations and river discharge in the 18-km reach downstream of the dam affected route-specific passage and survival. We found evidence of direct mortality associated with dam passage and indirect mortality associated with migration through the reach below the dam. Survival of fish passing over a surface spill gate (the west gate) was positively related to river discharge, and survival was similar for fish released below the dam, suggesting that passage via this route caused little additional mortality. However, survival of fish that passed under a sub-surface spill gate (the east gate) was considerably lower than survival of fish released downstream of the dam, with the difference in survival decreasing as river discharge increased. The probability of fish passing the dam via three available routes was strongly influenced by dam operations, with passage through the juvenile fish bypass and the east gate increasing with discharge through those routes. By simulating daily passage and route-specific survival, we show that variation in total survival is driven by river discharge and moderated by the proportion of fish passing through low-survival or high-survival passage routes.

Survival implications of diversion entrainment for out‐migrating juvenile Chinook Salmon and steelhead

“…Fish injury or death could occur at these locations when the opening is relatively small, which may increase the likelihood of fish striking the gate, encountering unsafe hydraulic conditions, or being injured by debris that accumulates or collects immediately downstream of the gate. There is evidence to support this theory from a previous study (Perry et al 2016) at Roza Dam, located upstream of our study area on the Yakima River. During that study, researchers found that fish survival through the East Gate, which operates similarly to a radial gate, declined severely during low-flow operations when the gate opening was greatly reduced (Perry et al 2016).…”

“…Fish that are eventually screened from the canal and returned to the river must also interact with several infrastructure components (trash racks, fish screens, bypass pipes), which could also result in injury or death. During the Perry et al (2016) study, survival through the fish bypass at Roza Dam was found to be the lowest of all passage routes across the entire range of streamflows and dam operations. Additionally, other fish species such as Northern Pikeminnow Ptychocheilus oregonensis, Smallmouth Bass Micropterus dolomieu, Channel Catfish Ictalurus punctatus, and Black Crappie Pomoxis nigromaculatus have been observed in canals on the Yakima River and present a constant predation threat to entrained juvenile salmon and steelhead (Beals and Lampman 2020).…”

“…Resource managers and stakeholders in the Yakima River basin have been adaptively responding to the results of these and other fish passage studies. For example, research conducted in reaches upstream of our study area during 2012-2016 identified route-specific passage issues that influenced out-migration survival at Roza Dam (Kock et al 2016;Perry et al 2016) and a flow-survival relationship in the Roza Reach of the Yakima River, downstream of Roza Dam (Courter et al 2016). Resource managers used this information to increase minimum instream flows targets in the Roza Reach and implement operational changes at Roza Dam to improve fish survival by reprogramming the gate operations to maximize surface spill over the West (right bank) Gate, which was shown to be the safest route of passage by Perry et al (2016).…”

“…Fish that are entrained into unscreened canals can be lost to the natural population (Post et al 2006;Perry et al 2015), and fish screens and bypass systems are rarely 100% effective at locations where these structures exist (Simpson and Ostrand 2012). Entrained fish may be exposed to piscivorous predators that reside in canals (Beals and Lampman 2020) and to other factors that increase mortality (Perry et al 2016). Additionally, water withdrawal results in decreased streamflow in downstream river reaches, negatively affecting aquatic communities in these reaches (Grantham et al 2010;Walters et al 2013;Ruhi et al 2016).…”

Integration of juvenile habitat quality and river connectivity models to understand and prioritise the management of barriers for Atlantic salmon populations across spatial scales

“…The potential impacts of PMBs are often ignored, despite increasing recognition of the potential impacts they pose to migratory fish species (Gowans et al 2003;Scruton et al 2007;Perry et al 2016;Nyqvist et al 2017b;Ovidio et al 2017). This likely reflects the high uncertainty that exists in defining the fish passage efficiency of particular passable barriers (Bunt, Castro-Santos & Haro 2012;Noonan, Grant & Jackson 2012).…”