Global Warming and Coldwater Fish
Coldwater fish are extremely sensitive to changes in water temperature.
When streams get too warm, the fish can experience:
- Slower growth rates
- Lower oxygen levels in the water
- Greater susceptibility to poisons, parasites and disease
If the water stays too warm for too long, the river will no longer provide a suitable home for the fish.
Pacific Northwest Rivers Heating Up
Research highlighted in the National Wildlife Federation report, Fish Out of Water: A Guide to Global Warming and Pacific Northwest Rivers, shows that a 3 degree rise in average August temperatures would cause up to 20 percent of the streams in the Columbia River Basin and coastal watersheds of Washington and Oregon to become too warm for most salmon, steelhead and trout.
If streams in the region continue to be degraded by other factors, the impact will likely be even greater.
Changing Flows Creating Obstacles for Spawning Fish
Earlier peak river flows in the spring (caused by earlier or more rapid snowmelt) and lower-than-normal flows in the summer can make it difficult for adult fish returning from the ocean at their usual time to negotiate obstacles such as falls as they navigate up stream to spawn.
These changes can also hinder the ability of juvenile fish to make it to the ocean. High river flows in the winter can cause "scouring," when the gravel beds that salmon eggs are laid in are washed away. On the other hand, too little water after spawning can harm the eggs.
Scientists project that, within just a few decades, without a significant reduction in the pollution that is contributing to global warming, the Pacific Northwest could face:
- even less winter snow accumulation;
- earlier peak spring streamflows;
- lower summer streamflows; and
- elevated stream temperatures.
Given the region's dependence on snowpack as the primary source of inflow to its surface water supplies, global warming is likely to dramatically alter the Pacific Northwest's rivers.
These potential changes do not bode well for cold-water fish like salmon, steelhead and trout--particularly those in rivers and streams that are also degraded due to dams, loss of riparian vegetation, water diversions and other problems.
Human activities already have pushed many stocks to the brink of extinction. With the added stress of global warming, the result could be devastating.