Climate Change Threatens Salmon Habitats within the US

Climate Change Shrinks and Fragments Salmon Habitats in a Snow-Dependent Region

Daniele Tonina, James A. McKean, Daniel Isaak, Rohan M. Benjankar, Chunling Tang, Qiuwen Chen

Summarized by Michael Hallinan

What data was used? The EAARL (Experimental Advanced Airborne Research Lidar) was used to collect the majority of the data. This machine rapidly outputs green lasers through air as well as water, which collects location and elevation when the reflection of each laser pulse is detected. This machine was used to survey Bear Valley Creek, an essential Chinook salmon (Oncorhynchus tshawytscha) spawn point located in Idaho, U.S.A. In addition to this, a series of habitat suitability curves (data expressing the ability of a species to live on observed environmental conditions) from the Washington Department of Fish and Wildlife was also used.

Methods: The location and elevation data allowed the local topography to be mapped. A series of hydrologic models and climate models were applied to the region with this topographical data, allowing the researchers to calculate surface area, volume, and mean depth of nearby bodies of water which are essential for early salmon development. In addition to this, hydraulic data such as velocity of water, depth, and shear stress (stress from water moving downstream) was predicted using these models for the entire year. All the modeled hydrologic, topographic, and geologic data were compared to the habitat suitability curves allowing to predict the quality of potential habitats in regards to salmon sustainability and upbringing as well as the distribution and connectivity of these habitats for salmon. 

Results: Between 1957-2016 it was found that average water flow has declined by 19%, or about 3% per decade. High water flow is essential for salmon to migrate in and out of streams. In addition, the velocity of the water also showed a decrease of 17% with the largest drops occurring in areas where salmon spawning is most frequent. As a result of these changes in water movement throughout these streams, there also was a clear negative impact on habitat conditions. It was found that the suitable spawning area for the salmon has significantly decreased. It’s expected that future summer water flow will be 72% lower than previously which will result in an approximate 38% decrease in spawning habitat size. Overall, climate change has shown to generate more negative conditions for salmon spawning as well as future negative impacts on habitat distribution. This can potentially threaten the long-term health of Chinook Salmon within this region, especially as they are already challenged by overfishing, these conditions could permanently damage the population’s health.

A colored figure displaying spawning habitat quality distribution for chinook salmon when water flow is at 1 cubic meter per second. Values go from 0 to 1 with 1 being the highest quality and 0 being the lowest. The river meanders in a snake-like shape going from the north-eastern part of the map to the south-eastern part of the map. Much of the water near the banks of the river features a spawning quality of 0, detailed in red. However, the more central parts of the river bed tend to fall within the 0.5 to 0.6 range with irregularly distributed sections within the 0.9 - 1 range throughout the river. This means that spawning habitat quality is generally very low near the edge of the river and mediocre through much of the river with higher quality occurring only in the center.
Figure displays an approximately 0.5km long segment of the Bear Valley Creek. distribution of Chinook salmon spawning habitat quality when water flow is at 1 cubic meter per second. The higher the quality value the more favorable to spawning, the lower the value the less favorable for spawning.

Why is this study important? Climate change has been shown to pervasively affect life on earth for example by changes in temperatures. Although within recent decades more progress has been made on our understanding of the topic, much of the current research still focuses on stream water temperature while other hydrological conditions that may significantly impact species health remain understudied. This study looks at these deeper hydrological conditions within the northwestern U.S, specifically in the Bear Creek region of Idaho, which is essential for the larger salmon population across the country and the fishing industry that depends on them. By increasing our understanding of these conditions and the impact of climate change, we can react better and begin to remediate these changes to support salmon populations as well as the local and global economies that depend on them. 

The big picture: Climate change has negatively affected salmon health and populations within the Bear Creek region of Idaho, U.S.A. This has been identified previously, but is usually only looked at within the context of temperature changes. This study further explores hydrological data and how it affects salmon reproduction, such as flow, velocity, and water depth. A 10% decrease in suitable spawning spaces was identified when comparing the likelihood of use as well as a 17% drop in flow velocity which negatively influences migration among stream for salmon. All of these factors threaten salmon populations, however being able to identify these may allow us to better understand salmon health as well as how to react in terms of conservation.

Citation: Tonina, D., McKean, J. A., Isaak, D., Benjankar, R. M., Tang, C., & Chen, Q. (2022). Climate change shrinks and fragments salmon habitats in a snow‐dependent region. Geophysical Research Letters, 49(12). 

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