Evaluation of the Biological Effects of the Northwest Power Conservation Council's Mainstem Amendment on the Fisheries Upstream and Downstream of Libby Dam, Montana, 2007-2008 Annual Report.

Sylvester, Ryan; Stephens, Brian E.; Tohtz, Joel

doi:10.2172/962397

Cited by 1 publication

(1 citation statement)

References 37 publications

(47 reference statements)

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“…Diet differences between large and small Rainbow Trout may also partially explain why D. geminata disproportionately influenced smaller Rainbow Trout growth rates. Sylvester and Stephens (2012) characterized Kootenai River Rainbow Trout diets using stable isotope techniques and found a prominent shift toward piscivory when fish grew to 300–400 mm TL. Smaller Rainbow Trout that rely primarily on invertebrates were likely differentially influenced by high winter D. geminata cover due to the smaller body size and lower caloric content of dipteran prey items available to fish during years with high D. geminata cover and/or the increased search time required to locate and prey on preferred larger but less abundant mayflies and caddisflies.…”

Section: Discussionmentioning

confidence: 99%

Factors Influencing Rainbow Trout Annual Growth in a Large Regulated River

Dunnigan

Terrazas

2021

Trans Am Fish Soc

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The construction and operation of dams represents one of the most significant anthropogenic impacts to the aquatic environment of freshwater ecosystems and includes changes in flow, temperature, water chemistry, sedimentation, and nutrient delivery. Despite the substantial changes caused by dams, we have a limited understanding of how dams influence important rate functions of fish, including growth rates. This study measured the growth rates of Rainbow Trout Oncorhynchus mykiss from successive captures of individually marked fish over seven annual increments within four river sections downstream of Libby Dam on the Kootenai River, Montana. We modeled the influence of hydropower‐related environmental variables on Rainbow Trout length and weight growth rates using linear mixed‐effects models. The top models predicting annual length and weight growth rates contained measures of water chemistry (ratio of total N to total P [N:P]) during the growing season, winter substrate coverage by the diatom Didymosphenia geminata, and an interactive term between winter D. geminata coverage and fish size at tagging. Winter D. geminata coverage and N:P were negatively correlated with annual growth rates, but the interactive term indicates that the influence of winter D. geminata coverage disproportionally affects smaller fish more than larger fish. We hypothesize that N:P and D. geminata are influencing Rainbow Trout growth rates through lower‐trophic‐level impacts. Top Rainbow Trout length and weight growth models explained 94.6% and 92.2%, respectively, of the annual variability in growth rates, of which 87.7% and 76.2%, respectively, were attributable to fixed effects. An experimental nutrient addition study and robust trophic monitoring efforts in the Kootenai River downstream of Libby Dam would be an effective means of independent corroboration of these study results. If successful, nutrient addition may be an effective management strategy to improve annual Rainbow Trout growth rates, mitigating for the nutrient retention occurring in the large reservoir upstream of Libby Dam.

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Section: Discussionmentioning

confidence: 99%