New research from Oregon State University shows that warm-water habitats can be critically important for the survival of cold-water fish like trout and salmon.
Amid climate change, this research has important implications for habitat protection and restoration efforts, which traditionally prioritize cold water bodies over those that warm during the summer months. , the researchers said.
“We show in this article that by devaluing hot habitats in summer, we miss their critical functions at other times of the year,” said Nick Hahlbeck, who led the research as a doctoral student at Oregon. State. “In this case, the habitat that would be written off provides almost all of the energy for growth and reproduction that is expressed at other times of the year.”
The research, recently published in the journal Conservation Biology, was conducted in Upper Klamath Lake in southwestern Oregon. This site is important because right now it is an example of what scientists fear is happening to other watersheds as the climate continues to warm, the researchers said.
âThe lake is 80 degrees Fahrenheit in the summer and neon green with algae blooms that can kill even the toughest species of fish. It’s the opposite of what we think of as trout habitat, âsaid Jonny Armstrong, an Oregon State ecologist and co-author of the article. “This research shows that habitat that is nasty in summer can be critically important in other seasons.”
The research focused on the salmon-sized red-banded rainbow trout, which is an important recreational fish and is the last subsistence fishery for the Klamath tribes. Previously, salmon were common in the area, and the research provides insight into how salmon might use the lake again once the dams are removed downstream, which could happen in the near future.
Scientists tagged around 100 redbanded trout and tracked their movements over three years. They measured the condition of the fish using a metric similar to body mass index and studied the contents of their intestines to calculate energy levels.
The intestinal contents indicated that the trout used the lake as a feeding ground in the spring and fall, consuming mainly fish. In contrast, the summer rations for trout were much smaller and consisted mainly of insects from the cold water tributaries of the lake. The differences in ration size and diet composition between the two habitat types amounted to a difference of about 100 times the energy consumed by a typical fish.
At least 65% of the tagged fish migrated to the lake twice a year between life spans in the tributaries for spawning or to escape the warm waters of the lake. Migration distances to the lake from cold water areas extended up to 30 miles and 90 miles from spawning grounds.
In the summer, 72% of the trout sampled were on an almost empty stomach, compared to only 10% of the trout sampled in the spring or fall, when most trout gorged themselves on small fish in the lake. On average, fish gained weight during residence periods in spring and fall and lost weight at similar rates in tributaries in subsequent seasons.
âWe have found that the fish use cool, clear tributaries, which resemble classic trout habitat, to take refuge in the summer and spawn in the winter, but their fall and spring feed in the lake is this. that pays the bills for the energy they spend in those other seasons, âsaid Armstrong, assistant professor in the College of Agricultural Sciences Department of Fisheries and Wildlife.
Planning for continued climate change often focuses on conserving habitat that could serve as so-called refuge, areas in which organisms can survive during a period of adverse conditions, the researchers said. They argue that this ignores the fact that mobile populations, such as redbanded trout, benefit from multiple habitats in a landscape, and that areas that would not be considered refugia may be vital.
“Our study empirically demonstrates that warm habitats can fuel cold-water fishing and challenges the common practice of identifying refugia based solely on summer conditions,” the researchers wrote. “The search for climatic refuges should be broadened to consider the suite of complementary habitats that mobile animals can connect in space and time.”
The other authors of the article are: Jordan Ortega, State of Oregon; William Tinniswood, Matthew Wyatt, Mark Hereford, Ben Ramirez, and Kara Anlauf-Dunn, all from the Oregon Department of Fish and Wildlife; Matthew Sloat, Wild Salmon Center, a Portland-based nonprofit; and David Crook, Center for Freshwater Ecosystems, La Trobe University, Australia.