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Stream habitat changes affecting primary consumers often indirectly impact secondary consumers such as fishes. Blooms of the benthic algae Didymosphenia geminata (Didymo) are known to affect stream macroinvertebrates, but the potential indirect trophic impacts on fish consumers are poorly understood. In streams of the Kootenai River basin, we quantified the diet, condition, and growth rate of species of trout, char, and sculpin. In 2018, macroinvertebrate taxa composition was different between a stream with Didymo and a stream without, but trout diets, energy demand, and growth rates were similar. Trout abundance was higher in the stream with Didymo, but the amount of drifting invertebrates was higher in the stream without. In 2019, we surveyed 28 streams with a gradient of coverage. Didymo abundance was correlated only with the percentage of aquatic invertebrates in trout diets and was not related to diets of char or sculpin or condition of any species. Thus, we found no evidence for a trophic link between Didymo blooms and the condition or growth of trout, char, or sculpin in mountainous headwater streams. Les modifications des habitats de cours d'eau qui ont une incidence sur les consommateurs primaires ont souvent des effets indirects sur les consommateurs secondaires comme les poissons. S'il est etabli que les proliferations de l'algue benthique Didymosphenia geminata (didymo) ont une incidence sur les macroinvertebres lotiques, leurs impacts trophiques indirects potentiels sur les poissons consommateurs ne sont pas bien compris. Nous avons quantifie le regime alimentaire, l'embonpoint et le taux de croissance de truites, d'ombles et de chabots dans des cours d'eau du bassin de la riviere Kootenai. En 2018, un cours d'eau ou l'algue didymo etait presente et un autre dont elle etait absente presentaient des compositions taxonomiques de macroinvertebres differentes, alors que les regimes alimentaires, la demande energetique et les taux de croissance des truites y etaient semblables. L'abondance de truites etait plus grande dans le cours d'eau contenant des algues didymo, mais la quantite d'invertebres a la derive etait plus grande dans le cours d'eau exempt de l'algue. En 2019, nous avons inventorie 28 cours d'eau definissant un gradient de couverture par l'algue didymo. L'abondance des algues etait seulement correlee au pourcentage d'invertebres aquatiques dans le regime alimentaire des truites et n'etait pas correlee au regime alimentaire des ombles ou des chabots, ni a l'embonpoint d'aucune espece. Ainsi, nous n'avons releve aucune preuve d'un lien entre les proliferations d'algues didymo et l'embonpoint ou la croissance des truites, ombles ou chabots dans des cours d'eau superieurs de montagne. [Traduit par la Redaction], Introduction Trophic structure determines the availability of food resources to organisms within a food web. The growth of these organisms depends not only on the amount of energy in a [...]

Hydropower has long been an effective form of renewable energy, but the development of the resource has negatively impacted fishes throughout the world. Formulating recovery plans to mitigate these effects requires a firm understanding of species‐specific provenance, life history and life stage habitat requirements. However, the importance of this information is often only recognised after a substantial population decline, when obtaining it becomes demographically challenging. We provide a case study for this scenario and present a post hoc approach to gain insight into these critical data gaps for Burbot Lota lota in the upper Kootenai River in Montana and British Columbia. The population once supported a robust tribal and recreational harvest but declined following impoundment and these fisheries have remained closed or curtailed for nearly 20 years. The reasons for the decline are unknown and actions to assist recovery have been constrained by limited information regarding natal origin, life history and habitat use. We addressed this issue using strontium isotope ratios (87Sr/86Sr) in otoliths collected over four decades in Lake Koocanusa, the reservoir on the Kootenai River above Libby Dam. Due to the geologic heterogeneity of the basin and resulting variation in water 87Sr/86Sr, the assignment probability for Burbot to their region of natal origin approached unity. Otolith 87Sr/86Sr also indicated the population was comprised of mainstem‐ and tributary‐origin forms and their relative abundance changed over time. Mainstem Burbot was most abundant during the 1970s and 2000s, whereas tributary forms dominated between these periods. We suggest ecosystem changes following impoundment contributed to this shift in life history forms and the overall decline of the population. Our findings underscore the need for additional investigations of these impacts to guide restoration efforts. [ABSTRACT FROM AUTHOR]

Research on fishes sometimes requires that individual fish be captured and subjected to invasive procedures multiple times over a relatively short time span. Electrofishing is one of the most common techniques used to capture fish, and it is known to cause injury to fish under certain circumstances. We evaluated the relationship of growth rates in Columbia River Redband Trout Oncorhynchus mykiss gairdneri to the number of times that they were captured via electrofishing and gastrically lavaged during the summer of 2018 in a mountainous, headwater stream. We captured fish between two and seven times over the course of 86 d using continuous (smooth) DC backpack electrofishing. We observed no relationship between the growth rate of Columbia River Redband Trout and the number of times that they were captured or gastrically lavaged. Although these findings contrast with hatchery electrofishing experiments, they may represent the greater resiliency of wild fish. It appears that researchers can use electrofishing and gastric lavage in cold waters at least once per month, and potentially up to twice per month, without greatly affecting the growth of wild Columbia River Redband Trout. [ABSTRACT FROM AUTHOR]