Use of Electromyogram Telemetry to Assess Swimming Activity of Adult Spring Chinook Salmon Migrating Past a Columbia River Dam

—Electromyogram (EMG) radiotelemetry was used to estimate the swim speeds of spring Chinook salmon Oncorhynchus tshawytscha migrating upstream past a Columbia River dam. Electrodes from EMG transmitters were surgically implanted in the red muscle of fish captured at Bonneville Dam, and output from the tags was calibrated to defined swim speeds for each fish in a tunnel respirometer. The fish were then released below Bonneville Dam and radio-tracked as they migrated through the tailraces, fishways, and forebays of the dam. On average, swim speed was significantly higher when tagged salmon were moving through tailraces than when they were moving through other parts of the dam. Specifically, swim speeds for fish in tailraces (106.4 cm/s) were 23% higher than those of fish in fishways (84.9 cm/s) and 32% higher than those of fish in forebays (80.2 cm/s). Swim speeds were higher in fishways during the day than during the night, but there were no diel differences in swim speeds in tailraces and forebays. During dam passage, Chinook salmon spent the most time in tailraces, followed by fishways and forebays. Pacific salmon Oncorhynchus spp. are known for their long spawning migrations. The freshwater stage of this upstream migration marks a change in the intake and allocation of energy. Instead of actively feeding and growing as they did during their oceanic phase, the salmon cease feeding once in freshwater and mobilize some of their energy reserves to gonad development. They use a substantial amount of their remaining energy reserves to fuel locomotory processes required for upstream migration (Greene 1926; Brett 1995). Much research on the behavior of adult Pacific salmon during their spawning migrations has been conducted (see reviews by Dauble and Mueller 2000 and Lucas and Baras 2001). Within the Columbia River basin, where hydroelectric development has significantly altered the migration corridor, thousands of adult salmon are implanted with radio transmitters during most years and their locations are tracked during their spawning migration (Boggs et al. 2004; Keefer et al. 2004a). These studies have shown that fish can be delayed at or fall back over dams and can have difficulty finding entrances to fishways. Delay of adult salmonids at dams can last for hours or days and can expose fish to increased predation by marine mammals, harvest by anglers, or mortality due to other sources (Dauble and Mueller 2000). The inability of fish to locate fishway entrances is a type of delay and results from the numerous sources of water discharge in the dam tailraces that act as attraction flow and confuse salmon (Bjornn et al. 1995). Fallback occurs when salmon ascend dams successfully but later end up downstream of the dam, requiring a repeat ascent (Liscom et al. 1985; Swan et al. 1994; Boggs et al. 2004). For example, from 1996 to 2001, at least 22% of radio-tagged spring and summer Chinook salmon O. tshawytscha that passed a dam fell back over at least one dam while migrating up the Columbia and Snake rivers (Boggs et al. 2004). Delay and fallback at dams may deplete the limited energy reserves of upstream-migrating adult salmonids, perhaps leaving them with insufficient reserves for gonad development and successful spawning. However, little is known about the behavior associated with dam passage in adult salmonids. Thus, to address this information gap, we conducted a 1-year study based on the use of electromyogram (EMG) radiotelemetry to estimate the swim speed of Chinook salmon passing Bonneville Dam, the lowermost dam on the Columbia River. Although EMG telemetry has been used to examine the behavior and energy use of Pacific salmon in free-flowing rivers (Hinch et al. 1996; Hinch and Rand 1998; Rand and Hinch 1998; Hinch and Bratty 2000; Brown and Geist 2002), this technology has not * Corresponding author: [email protected] Received October 28, 2004; accepted October 1, 2005 Published online February 8, 2006 281 Transactions of the American Fisheries Society 135:281–287, 2006 Copyright by the American Fisheries Society 2006 DOI: 10.1577/T05-223.1 [Article] D ow nl oa de d by [ Pa ci fi c N or th w es t N at io na l L ab s] a t 1 2: 13 1 3 D ec em be r 20 13 been used to estimate salmon swimming behavior associated with dam passage. Specifically, our objectives were to (1) describe the movements and behavior of adult spring Chinook salmon as they approached and passed the dam and (2) estimate the swim speed of spring Chinook salmon as they passed through the tailraces, fishways, and forebays of the dam. Information on the activity of salmon as they migrate through a dam should aid managers in modifying or deriving new fish protection measures to improve recovery of populations listed under the federal Endangered Species Act.