Chasing the cold: Thoughts on moving trout in warming world

Record summer heat and an ongoing drought make for tough conditions for our country's trout and salmon.

By Jack Williams

The summer of 2015 was a hot one by almost any measure. According to NOAA, July was the warmest month since record-keeping began in 1880 and was 1.46 degrees Farenheit above the 20th Century average. Record heat combined with a multi-year drought in much of the West to produce some of the lowest and warmest river flows early in the season, resulting in substantial fish kills up and down the West Coast. 

Anglers and agencies alike called for fishing restrictions to help save stressed fish. In some places, salmon were trucked around hot water in downstream rivers to cooler headwater streams. It was a tough summer and one that is likely to become all too common in the future.     

What to do? How can we help our trout and salmon survive these conditions?

Scientists are experimenting in Montana by moving bull trout into high-elevation waters to protect them from warming waters.

One proposed solution is to translocate trout and salmon from their native range into cooler waters outside that range.   

Recently, federal fishery scientists in Montana were in the news for moving bull trout to cooler headwater streams. In this case, bull trout, were kept within their native watersheds but were moved upstream above impassible natural barriers to higher-elevation streams and lakes that are more likely to remain cool in the future. At this small scale, it’s more like an experiment than a novel management strategy, but it begs the question: Should we move these fish to cooler water they never inhabited to help them escape the warming water within their native range?

There are many good reasons to move slowly—if at all—in translocating fish beyond their native range. For one, there is no such thing as a vacant habitat. What becomes a transplant for one species becomes an invasion for others. How will the species already present be impacted by the introduction of a new fishy predator? Some amphibian populations, for example, have been eliminated by fish introductions where no fish predator had been before. Also, as we move trout into smaller isolated headwater areas, we produce small populations that may be increasingly vulnerable in their own right to genetic bottlenecks or increasing disturbances like wildfire or floods. Further, we reduce life history choices, such as the ability to migrate and readily move from one stream system to another. One of the reasons that trout and salmon have been so successful in their evolutionary history is their ability to produce individuals with diverse life histories – some fish migrate long distances while others stay at home. Some that spawn in lakes while others spawn in streams.  

Outgolng salmon smolts could be met with poor ocean conditions thanks to warming waters, and migrating adult salmon could face warm, inhospitable waters on their way to their natal spawning streams.

But just because we pause on the question of translocations doesn’t mean we should sit on our hands. Far from it. We should use the data from projects like the Cold Water Climate Shield and stream temperature networks to make sure we are focusing our restoration efforts in those habitats that will have the best chance of supporting trout and salmon in the future. We must tackle the problems we can—especially those like overgrazing, excess road construction or poor road maintenance, or poorly designed culverts—to reduce the cumulative stress facing our trout and salmon during times of rapidly changing climate. We are being successful in restoring Yellowstone cutthroat trout in Yellowstone Lake, which at a high elevation offers a good chance of maintaining cold water habitat in a warming world. Persistent efforts by the National Park Service, USGS scientists and Trout Unlimited are controlling introduced lake trout that have preyed heavily on the native cutthroat.  

We are making progress in our adaptation and recovery efforts in many important places. We recently reviewed climate change adaptation for western trout streams to learn what strategies work best, and found some stunning successes when climate problems were addressed head on and work occurred across entire watersheds.    

That’s not to say that we should completely avoid experimental translocations like what occurred recently with bull trout in Montana. But these efforts are best when viewed as learning experiments and they must be carefully monitored to see what impacts we are producing not only for the species being moved but also for those native to the system.

While considering every option to protect our trout and salmon from a warming world is important, we must address the root causes of climate change, and reduce our emissions of greenhouse gases.

Of course, if we don’t get our act together and start reducing greenhouse gases in the atmosphere and in the oceans, future generations are likely to have bigger problems to face than poor trout fishing. Ultimately, we must tackle the roots of these problems not just the symptoms. Our ability to find technological solutions to environmental problems is much more limited than we would like to believe.

Changing ocean conditions illustrate our inability to manage our way out of certain problems. Unusually warm water—known as “the blob”—now stretches along the West Coast from central Mexico to Alaska. Tropical sea snakes are appearing off the California Coast. Off the British Columbia Coast, scientists are recording the hottest ocean temperatures ever, with temperatures that might statistically be expected only once every 400 years.

We simply do not have models that are going to accurately predict how the ocean will behave under these kinds of conditions. The temperatures are off the charts. This means that migrating salmon and steelhead enter freshwater in poorer condition as they swim farther around nutrient-poor warm ocean waters to reach freshwater rivers. More importantly, out-migrating juvenile salmon and steelhead will face a hot, unproductive ocean that is void of the normal cold-water upwelling that brings small food organisms from the depths to feed the growing fish. That can be fatal for the young fish. If these conditions occur in successive years, we will start to lose entire stocks of salmon and steelhead.

That is a problem that fisheries science cannot solve.  

Jack Williams is TU's senior scientist. He is based in Medford, Ore.



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