Rainbow trout Oncorhynchus mykiss energetic responsesto pulsed flows in the American River, California, assessed by electromyogram telemetry

Abstract

Although rainbow trout Oncorhynchus mykiss within the American River, California, apparently exhibit minimal upstream or downstream movements in response to hydroelectric-power-generation-related pulsed flows, the associated energetic costs are unknown. We implanted rainbow trout (n=9, ≥30 cm SL) with electromyogram (EMG)-sensor-equipped radio transmitters to assess the swimming behavior and associated energetic costs associated with their responses to pulsed flows. Using laboratory calibrations in a Brett-type swimming respirometer, the trouts' swimming speeds and oxygen consumption rates were estimated for their in-river EMG data, through a complete hydroelectric power-generation river pulsedflow sequence (pre-pulse, increasing flow, peak, and decreasing flow stages), on several (mean: 3.2) sampling dates. Using a mixed-linear model, we found that fish swimming speed estimates increased during the increasing flow stage, while the associated mean oxygen consumption rates also increased at this stage. At river flows near the usual peak (>44 m ), swimming speeds and movement rates decreased, possibly due to the fish using the river's habitat complexities as hydraulic cover. We conclude that rainbow trout incur increased swimming-related energetic costs during increasing flows and, potentially, decreased foraging opportunities at high flows.

HYDROLOGIC CORRELATES OF BULL TROUT (Salvelinus confluentus) SWIMMING ACTIVITY IN A HYDROPEAKING RIVER

“…Similarly, Murchie and Smokorowski () found that periods of changing discharge (up‐ramping and down‐ramping) had no greater effect on activity than relatively stable discharges in the Magpie River, Ontario. A number of other studies have found no effect of short‐term changes in river discharge on fish movement when locating fish at weekly (Cocherell et al ., ), daily (e.g. Broadhurst et al ., ) and subdaily scales (e.g.…”

Response of two-spined blackfish Gadopsis bispinosus to short-term flow fluctuations in an upland Australian stream

“…Neither brook trout Salvelinus fontinalis nor walleyes Sander vitreus moved in response to a flow release, but the activity of both species increased with discharge (Murchie & Smokorowski, 2004), presumably in response to increased efforts to maintain position. Similarly, rainbow trout increased their energetic output during increasing flows (Cocherell et al, 2010). Although, once peak flow had been reached, these trout decrease their energetic output, suggesting that individual fish take refuge and cease foraging during peak flows (Cocherell et al, 2010).…”

“…Similarly, rainbow trout increased their energetic output during increasing flows (Cocherell et al, 2010). Although, once peak flow had been reached, these trout decrease their energetic output, suggesting that individual fish take refuge and cease foraging during peak flows (Cocherell et al, 2010). It is likely that movement and activity of benthic fish species is less likely to change in response to increased flow, when compared to pelagic species.…”

“…Such responses have been found for pelagic species (e.g. Murchie & Smokorowski, 2004;Cocherell et al, 2010), but the response of benthic species has received negligible research attention. Displacement of two-spined blackfish from elevated flows is unlikely, due to the proclivity for instream cover (Lintermans, 1998(Lintermans, , 2007 and the species' capability of occupying the boundary layer within the cobble-boulder stream bed.…”

“…Monitoring of the shortterm responses of fishes to flows released from dams has primarily been conducted using implanted radio transmitters to analyse changes in movements or activity following releases from hydroelectric dams (e.g., Geist et al, 2005;Scruton et al, 2008;Cocherell et al, 2010). The responses of fishes during high natural flows, especially floods, have also been documented (David & Closs, 2002;Koster & Crook, 2008;Makiguchi et al, 2009).…”