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.

Keywords: behavioral thermoregulation; climate change adaptation; lotic ecosystem management; refugia; salmonids; temperature; thermal heterogeneity; thermal refuges.

FIGURE 1

Brown trout (Salmo trutta) observed behaviorally thermoregulating in a cold-water refuge (CWR) to avoid high water temperatures in the Upper Housatonic River in Connecticut, USA (a). Designated areas are closed to anglers and delineated by signs posted (b). Thermal infrared (TIR) image of the surface water temperature of the cold-water plume entering the river (c). Images courtesy of Christopher Sullivan and Nancy Marek, University of Connecticut, USA.

FIGURE 2

Linking science and policies to protect, enhance, and restore cold-water refuges and thermal heterogeneity: (a) identification of cold-water refuges through monitoring and modeling to map and prioritize areas of interest, (b) assessment of potential conflicts among interested groups to align policies and management, and (c) assessment of legal and institutional constraints by identifying direct and indirect management approaches and policies.

FIGURE 3

Overarching research gap themes, outstanding general questions, and proposed solutions to improve resilience of cold-water patches (CWPs) and cold-water refuges (CWRs).

FIGURE 4

Sequential approach to implement and evaluate science-based management and policies related to cold-water refuges and thermal heterogeneity.

FIGURE 5

Spatial alignment of policies and management strategies of cold-water refuges (CWRs). Example shows: (a) watershed with multiple jurisdictions and interested groups (as represented by different colors and boxes) with potentially conflicting values and objectives that lead to unstructured and inconsistent management and policies; (b) watershed as the planning unit, where strategies align to create a consistent management plan guided by common socioeconomic values and converging objectives of all interested groups (multiple jurisdictions and interested groups are still in place); and (c) scales of organization with corresponding management prioritization.

FIGURE 6

Triple-loop learning adaptive management approach showing the different pathways and outcomes of cold-water refuge (CWR) policies. Policy provides a baseline to support management, while implementing an adaptive management approach to account for the spatial and temporal variability of CWRs. Each loop involves reevaluating assumptions to decide whether to alter the decision-making framework. Figure adapted from Kittinger et al. (2011) and Morelli et al. (2016).