Danielle M. Frechette | USGS Science

USGS2025

Seaward movements and mortality of Atlantic salmon Salmo salar L. kelts in the Penobscot River, Maine

The Atlantic salmon Salmo salar L. is an endangered species in the United States, but post-spawn downstream movements remain poorly understood. We conducted a 2-year acoustic telemetry study to characterize downstream movements and to quantify apparent mortality and downstream passage of post-spawn adults (kelts) in the Penobscot River, Maine, USA ( N = 112). The majority of tagged S. salar kelts (54%) exhibited a rapid movement seaward post-release instead of overwintering in the river. Salmo salar kelts that overwintered exhibited two patterns, distinguished by whether a dam was present or not. We found no relationship between post-release movement pattern, sex, body condition index or release year. Estimated apparent mortality rates were high (83%), with a greater probability of mortality occurring near the dams and release site. Apparent mortality rate did not differ by sex, body condition or year, but it was greater for individuals that moved out directly post-release and less for those that overwintered. While our results may suggest that overwintering in the river is a favourable pattern for survival, these results may be related to the closures of the designated downstream passages at the first two dams encountered by S. salar kelts. In fact, 55% of S. salar kelts passed a dam when the designated passages were closed. Altogether, these results may demonstrate the complex nature of downstream passage for S. salar kelts, particularly when having to navigate multiple dams.

Penobscot River↗

USGS2023

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

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.

Global Change Biology↗