Closing the gap between science and management of cold‐water refuges in rivers and streams

Abstract

Human activities and climate change threaten coldwater organisms in freshwater ecosystems by causing rivers and streams to warm, increasing the intensity and frequency of warm temperature events, and reducing thermal heterogeneity. Cold‐water refuges are discrete patches of relatively cool water that are used by coldwater organisms for thermal relief and short‐term survival. Globally, cohesive management approaches are needed that consider interlinked physical, biological, and social factors of cold‐water refuges. We review current understanding of cold‐water refuges, identify gaps between science and management, and evaluate policies aimed at protecting thermally sensitive species. Existing policies include designating cold‐water habitats, restricting fishing during warm periods, and implementing threshold temperature standards or guidelines. However, these policies are rare and uncoordinated across spatial scales and often do not consider input from Indigenous peoples. We propose that cold‐water refuges be managed as distinct operational landscape units, which provide a social and ecological context that is relevant at the watershed scale. These operational landscape units provide the foundation for an integrated framework that links science and management by (1) mapping and characterizing cold‐water refuges to prioritize management and conservation actions, (2) leveraging existing and new policies, (3) improving coordination across jurisdictions, and (4) implementing adaptive management practices across scales. Our findings show that while there are many opportunities for scientific advancement, the current state of the sciences is sufficient to inform policy and management. Our proposed framework provides a path forward for managing and protecting cold‐water refuges using existing and new policies to protect coldwater organisms in the face of global change.

Disentangling effects of habitat on salmonid abundance in thermal refuges while accounting for imperfect detection

“…For the purposes of this investigation, we defined a "thermal refuge" as a cold-water patch in the main stem created by a groundwater-dominated tributary >2.0 C cooler than the main stem river and known to be used by fish for short-term thermal protection during periods of heat stress (i.e., tributary confluence thermal refuge defined by ambient water temperatures; Figure 2; Sullivan et al, 2021). The temperature differential threshold of 2.0 C used to delineate a thermal refuge is similar to other studies (e.g., Ebersole et al, 2003aEbersole et al, , 2003bGreer et al, 2019;Mejia et al, 2023). Importantly, thermal refuges are not frequently used by fish during other periods throughout the year, indicating that trout seek out these locations during summer heat waves.…”

“…Second, trout species-habitat relationships can vary to a degree across riverscapes (e.g., Al-Chokhachy et al, 2010). Thus, understanding thermal refuge characteristics leading to higher abundances of the aggregate of cold-water-dependent trout species will help identify dominant refuge characteristics and be of greater conservation relevance globally (e.g., Mejia et al, 2023). In addition, we omitted cool-water-dependent fish species that were not trout from the analysis (e.g., smallmouth bass Micropterus dolomieu and white sucker Catostomus commersonii) as they accounted for <0.001% of all counted fish.…”

“…Previous studies largely use data derived from tagged salmonid movements (Barret & Armstrong, 2022;Brewitt et al, 2017;Dugdale et al, 2016;Frechette et al, 2018;Ritter et al, 2020) or models describing habitat selection of the aggregate of thermoregulating trout (Wang et al, 2020;Wilbur et al, 2020) to describe refuge use patterns. Studies estimating abundance, a common analytical endpoint in ecology, of trout within thermal refuges are rare (see review in Mejia et al, 2023). Strange (2011) and Sutton et al (2007) used snorkeling surveys to count trout within thermal refuges in the Klamath River.…”

“…We also include covariates describing recent fluctuations in main stem river water temperatures since they can influence the thermal refuge-seeking behaviors of salmonids (O' Sullivan et al, 2023). To our knowledge, this is the first use of UAC surveys coupled with a hierarchical model to examine thermal refuge use by a cold-water-dependent trout (i.e., rigorously estimate abundance) while accounting for observational error, addressing a recently identified research gap (Mejia et al, 2023). Given the role that thermal refuges play in protecting cold-or cool-water-dependent fish against extreme hot temperature events, our results should better position managers for developing more proactive cold-water refuge conservation tactics with the goal of the long-term sustainability of cold-water-dependent trout in marginal riverscapes globally.…”

Predicting stream water temperature with artificial neural networks based on open‐access data

“…In light of climate change, such knowledge is also highly relevant for deducing mitigation and management strategies in streams related to securing high oxygen concentrations (Piatka et al, 2021), endangered fish populations (Wild et al, 2023), and temperature refuges (Kuhn et al, 2021;Mejia et al, 2023). In contrast to existing approaches, which mainly consider hyperparameter tuning and dataset length, the associations between environmental parameters and ANN accuracy allow a more mechanistic and realistic assessment of model applicability at individual stream sites, as demonstrated for our datasets.…”