Background Altering the natural flow regime, an essential component of healthy fluvial systems, through hydropower operations has the potential to negatively impact freshwater fish populations. Establishing improved management of flow regimes requires better understanding of how fish respond to altered flow components, such as flow magnitude. Based on the results of a recent systematic map on the impacts of flow regime changes on direct outcomes of freshwater or estuarine fish productivity, evidence clusters on fish abundance and biomass responses were identified for full systematic review. The primary goal of this systematic review is to address one of those evidence clusters, with the following research question: how do changes in flow magnitude due to hydropower operations affect fish abundance and biomass? Methods This review follows the guidelines of the Collaboration for Environmental Evidence. It examined commercially published and grey literature originally identified during the systematic map process and a systematic search update. All articles were screened using an a priori eligibility criteria at two stages (title and abstract, and full-text) and consistency checks were performed at all stages. All eligible articles were assessed for study validity and specifically designed data extraction and study validity tools were used. A narrative synthesis included all available evidence and meta-analysis using the standardized mean difference (Hedges’ g) was conducted where appropriate. Review findings A total of 133 studies from 103 articles were included in this systematic review for data extraction and critical appraisal. Most studies were from North America (60%) and were conducted at 146 different hydropower dams/facilities. Meta-analysis included 268 datasets from 58 studies, separated into three analyses based on replication type [temporal (within or between year replication) or spatial]. Fish abundance (226 datasets) and biomass (30 datasets) had variable responses to changes in flow magnitude with estimated overall mean effect sizes ranging from positive to negative and varying by study design and taxa. In studies with temporal replication, we found a detectable effect of alterations to the direction of flow magnitude, the presence of other flow components, sampling methods, season, and fish life stage. However, we found no detectable effect of these moderators for studies with spatial replication. Taxonomic analyses indicated variable responses to changes in flow magnitude and a bias towards salmonid species. Conclusions This synthesis did not find consistent patterns in fish abundance or biomass responses to alterations or changes in flow magnitude. Fish responses to flow magnitude alterations or changes were highly variable and context dependent. Our synthesis suggests that biotic responses may not be generalizable across systems impacted by hydroelectric power production and operations, where specific features of the system may be highly influential. Site-specific and adaptive management may be necessary. To improve study validity and interpretability, studies with long-term continuous monitoring, and both temporal and spatial replication are needed. When this gold standard is unfeasible, studies should strive, at minimum, to maximize replication within both intervention and comparator groups for either temporal or spatial designs. To further address knowledge gaps, studies are needed that focus on non-salmonids, multiple seasons, and systems outside of North America.
Effective management of freshwater fish habitat is essential to supporting healthy aquatic ecosystems and sustainable fisheries. In Canada, recent changes to the Fisheries Act enhanced the protection of fish habitat, but application of those provisions relies on sound scientific evidence. We employed collaborative research prioritization methods to identify scientific research questions that, if addressed, would significantly advance the management of freshwater fish habitat in Canada. This list was generated by a diverse group of freshwater fish experts, including substantial contributions from practitioners who administer provisions of the Fisheries Act. The research questions generated in this study identify priority topics for future research, while highlighting issues that could be addressed with different funding models. As a result, this study should support evidence-based management of Canada’s aquatic resources by identifying scientific knowledge gaps faced by practitioners, and suggesting funding mechanisms to address them. Given the important contribution of Canadian freshwater systems to global ecosystem values, and the similar scientific challenges facing fish habitat managers in other jurisdictions, this study is likely to have broad applicability.
We compared two passive wire traps for trapping wild crayfish-a trap designed specifically for capturing crayfish and a minnow trap commonly adapted for this purpose. We investigated crayfish capture efficiency, retention of captured crayfish, and capture of non-target finfishes for both trap types in mesocosm and field experiments. The crayfish traps captured more crayfish than the minnow traps in both settings. The minnow traps better retained captured crayfish; however, they also captured significantly more nontarget finfishes. We conclude that the crayfish trap performed better than minnow traps for the capture of wild crayfish.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.