Climate Change Emphasizes Importance of Cold-Water Habitats for Fish

In the Northwest, climate modeling predicts a shift in the timing and perhaps the quantity of precipitation, with less snow and more rain in the winter and warmer temperatures throughout the year.

These changes would threaten aquatic ecosystems, alter key habitat conditions for salmon and other cold water aquatic fish species such as trout and bull trout and, potentially, warm water to lethal temperatures – as happened in the Columbia last summer, and contribute to fish disease and mortality.

Research by the U.S. Forest Service, ongoing since 1968, shows river water and summer air temperatures are warming throughout the Northwest. What can be done to protect cold-water fish as the climate warms? 

In short, the best approach will be to focus on protecting and enhancing the habitat where fish spawn, rear, and migrate, Forest Service scientist Dan Isaak reported to the Council at a recent meeting. This would include, for example, planting more streamside vegetation that shades the water in spawning and rearing areas, and perhaps providing fish passage into areas of cold-water habitat that currently are blocked by dams or natural barriers. Other approaches could include taking steps to reduce the risk of wildfires in places where streamside vegetation could be destroyed, and purchasing water rights from willing sellers to leave more water in streams and rivers. 

Columbia River salmon are trying to adapt. For example, summer-migrating salmon like sockeye are returning from the ocean to spawn progressively earlier in the year. In the summer of 2015, some sockeye migrated though the interior Columbia River Basin before water temperatures became lethal, but an estimated quarter million died between Bonneville and McNary dams in July. 

Given the uncertainty of future climate conditions – generally, an increasing warming trend, but precisely how much warmer is a guess – Isaak said it is imperative to identify and protect what are called “climate refuge habitats.” Protecting these cold-water places, generally in the upland headwaters of rivers and streams, provides a hedge against the uncertainty of climate-change risk, he said. 

The Forest Service is using geographic information system data to model stream temperatures and fish distribution to find the best possible locations in the Northwest for these risk-hedging investments, an effort identified in the Council’s Columbia River Basin Fish and Wildlife Program. The program calls for evaluating the effectiveness and feasibility of possible actions to mitigate effects of climate change. 

Isaak said the warming future demands a different mindset, one that accepts the fact that some rivers will warm beyond our ability to slow the change, forcing us to accept that we can’t save everything. But we can commit to a determined, long-term effort to save the best places, he said.