The importance of warm habitat to the growth regime of cold-water fishes
Armstrong, J., A. Fullerton, C. Jordan, Joe Ebersole, J. Bellmore, I. Arismendi, B. Penaluna, AND G. Reeves. The importance of warm habitat to the growth regime of cold-water fishes. Nature Climate Change. Nature Publishing Group, New York, NY, , 00994, (2021). https://doi.org/10.1038/s41558-021-00994-y
Many rivers and streams supporting cold-water fish such as salmon and trout in United States are currently listed as impaired under the Clean Water Act as a result of high summer water temperatures. Adverse effects of warm waters include impacts to cold-water fish populations that may already be stressed by habitat alteration, disease, predation, and competition with other species. Much effort is being expended to improve conditions for species like salmon and trout, with increasing emphasis on protecting areas of cold water. This approach may devalue downstream habitats that are warmer during the summer months. Yet these downstream habitats may be extremely important to mobile cold water fishes during the fall, winter, and spring months when temperatures are more suitable. In this paper we provide a conceptual framework, the growth regime, that recognizes the growth potential value of riverine habitats across space and time. Our work reveals a strong synergy between cold and warm habitats that could be fundamental for supporting coldwater fisheries, yet is currently underappreciated in climate change adaptation planning.
A common goal of biological adaptation planning is to identify and prioritize locations that remain suitably cool during the summer. This implicitly devalues areas that are ephemerally warm, even if they are suitable most of the year for mobile animals. Here we develop an alternative conceptual framework, the growth regime, which considers seasonal and landscape variation in physiological performance, focusing on riverine fish. Using temperature models for 14 river basins, we show that growth opportunities propagate up and down river networks on a seasonal basis, and that downstream habitats that are suboptimally warm in summer may actually provide the majority of growth potential expressed annually. We demonstrate with an agent-based simulation that the shoulder-season use of warmer downstream habitats can fuel annual fish production. Our work reveals a synergy between cold and warm habitats that could be fundamental to support cold-water fisheries, and highlights the risk in conservation strategies that underappreciate warm habitats.