Climate change is shrinking and fragmenting salmon habitat
Salmon are famous for traveling hundreds of miles upstream to reach their home waters to spawn, but climate change is shrinking their destination. A new study provides high-resolution details about how Chinook salmon habitats are being lost on Bear Valley Creek, a headwaters of the Salmon River in central Idaho.
The study, published today in the AGU journal Geophysical Survey Letters, suggests that lower water volumes and warming temperatures dramatically shrink the spawning beds and nurseries for the culturally and economically important fish. Researchers predict that salmon here could lose nearly half of its total habitat in this river by 2040 due to an estimated 50% decrease in river discharge.
Daniele Tonina, lead author of the new study and professor of ecohydraulics at the University of Idaho, and colleagues examined a 14-kilometer stretch of Bear Valley Creek, known for housing a robust population of Chinook salmon. With a wide valley, meandering main river and cozy tributaries, the location is representative of ideal Pacific Northwest salmon habitats.
The team mapped the channels and floodplains of the river using a type of remote control, 3D laser scanning, or LiDAR, which uses green-wavelength lasers to see in shallow water environments. They then used 60 years of historical stream flow data, from 1957 to 2016, from stream meters at eight nearby streams to calculate trends in annual summer discharge, a critical time for fish survival. Using three different hydrological models to combine river characteristics and predicted discharge through 2090, they estimate changes in salmon habitat both in the past and in the coming decades.
During the historical study period, the volume of summer flow decreased by 19% and slowed down by 17%. This means less surface area generally suitable for salmon nests and loss of refuges for finger-fingered birds outside the channel as side streams are cut off from the main channel. About 20% of this critical habitat beyond the channel had already been lost in the 60-year span, the study estimates. The salmon also lost 23% of its spawning habitat.
“This allowed us to really understand how the environment will change with different discharges, which has not been done before. Now we can say that the impact will be that the habitat will become smaller and more fragmented, meaning that even the parts that are still good [quality] maybe too small to be useful,’ Tonina said. ‘Yet this is a half-full, half-empty result. In any case, it is not yet a total loss of habitat.”
“A huge limitation has been our ability to study the landscape at a scale that is biologically relevant to salmon,” said Lisa Crozier, a research ecologist at NOAA’s Northwest Fisheries Science Center, who was not involved in the study. “We know the general pattern is that low currents are bad for fish, but we don’t know exactly why or which life stages are most affected. But here we can see very specifically that they are losing off-channel and spawning habitat. It really helps to know those details.”
Storing salmon flows
Salmons make high demands on their nests. Each female can use up to six square feet of real estate in the riverbed to lay her eggs; the gravel must be just right, the water must be cold and flowing, there must be calm side streams for the fingers to grow. And, of course, enough water has to flow into the streams for the salmon to arrive in the first place. Every demand is threatened.
Smaller, lower quality salmon habitats can reduce spawning success and increase the struggle for young salmon, which already face many human-induced barriers. There may be more female salmon competing for shrinking nesting sites, and young salmon will also be competing for dwindling space and resources. Raising salmon whose home waters are cut off or disappear altogether can take too much energy to search for a new place and die of exhaustion before laying their eggs.
Studies like these are helping ecologists and conservationists figure out which areas are most likely to remain suitable habitats for salmon and other species, and therefore could be targets for protection, Tonina said. Other cold water fish, such as trout and steelheads, would be affected in similar ways. Chinook salmon serve as useful “indicators of massive ecosystem changes,” Crozier added, but “every species will be affected by these changes. It’s uncharted territory.”
“This will aid recovery efforts and help us select streams that are likely to remain accessible to the salmon,” Tonina said. “We want to find the areas that will serve as refuges in the future.”
Up to 85 percent of historic salmon habitat lost in the Lower Fraser . region
Daniele Tonina et al, Climate change is shrinking and fragmenting salmon habitats in a snow-dependent region, Geophysical Survey Letters (2022). DOI: 10.1029/2022GL098552
Quote: Climate Change Shrinks and Shreds Salmon Habitat (2022, June 28) retrieved June 29, 2022 from https://phys.org/news/2022-06-climate-fragmenting-salmon-habitat.html
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