Abstract
Little is known about the three-dimensional depth distributions in rivers of individually marked fish that are in close proximity to hydropower facilities. Knowledge of the depth distributions of fish approaching dams can be used to understand how vulnerable fish are to injuries such as barotrauma as they pass through dams. To predict the possibility of barotrauma injury caused by pressure changes during turbine passage, it is necessary to understand fish behaviour relative to acclimation depth in dam forebays as they approach turbines. A guiding study was conducted using high-resolution three-dimensional tracking results of salmonids implanted with Juvenile Salmon Acoustic Telemetry System transmitters to investigate the depth distributions of subyearling and yearling Chinook salmon (Oncorhynchus tshawytscha) and juvenile steelhead (Oncorhynchus mykiss) passing two dams on the Snake River in Washington State. Multiple approaches were evaluated to describe the depth at which fish were acclimated, and statistical analyses were performed on large data sets extracted from ∼28 000 individually tagged fish during 2012 and 2013. Our study identified patterns of depth distributions of juvenile salmonids in forebays prior to passage through turbines or juvenile bypass systems. This research indicates that the median depth at which juvenile salmonids approached turbines ranged from 2.8 to 12.2 m, with the depths varying by species/life history, year, location (which dam) and diel period (between day and night). One of the most enlightening findings was the difference in dam passage associated with the diel period. The amount of time that turbine-passed fish spent in the immediate forebay prior to entering the powerhouse was much lower during the night than during the day. This research will allow scientists to understand turbine-passage survival better and enable them to assess more accurately the effects of dam passage on juvenile salmon survival.
Highlights
Conservation and restoration of declining fish populations is a primary focus for many fisheries researchers and managers (MacIlwain, 1997; Wakefield, 2001; Miller, 2010)
Fish implanted with Juvenile Salmon Acoustic Telemetry System (JSATS) acoustic transmitters were detected using JSATS-cabled hydrophone arrays (Weiland et al, 2011) deployed on the dam faces of Little Goose Dam (LGS) (Fig. 2A) and Lower Monumental Dam (LMN)
Given that the primary purpose of this research was to estimate the depth where juvenile salmonids may be neutrally buoyant prior to turbine passage, their 3-D locations were treated in several different ways to see whether there was a difference among the approaches
Summary
Conservation and restoration of declining fish populations is a primary focus for many fisheries researchers and managers (MacIlwain, 1997; Wakefield, 2001; Miller, 2010). This focus has become increasingly important for river systems where hydropower facilities provide an obstacle for migratory fish passage or for areas where new hydro structures will be built, especially in areas where global human populations are expected to expand rapidly (Cooke et al, 2013a). Researchers have noted that, among juvenile salmonids, both large and rapid changes in pressure lead to barotrauma They suggest that barotrauma is largely related to the expansion and rupturing of the swim bladder (Brown et al, 2012). Understanding how fish are injured by barotrauma is directly related to the ratio of the volume of gas within the swim bladder of a neutrally buoyant fish before it enters a turbine (often termed the acclimation pressure; Pflugrath et al, 2012) and the lowest pressure to which the fish are exposed during turbine passage (often termed the nadir pressure)
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