Headwaters: Silver lining in a warming world?

Trout in many parts of West are being pushed into headwater streams by non-native species downstream. These streams are also warming slower than other stretches of western rivers. 
 
By Jack Williams
 
For those of us working to conserve trout and salmon in a warming world, we see a daily barrage of articles about increasing storm intensities, rising sea levels, ocean acidity, loss of mountain snowpacks, and the steady warming of our planet. There is plenty of bad news out there for salmon, trout, and the people who chase them with rod and reel.  
 
So, when some good news comes along, we tend to be befuddled; almost like deer in the headlights.  
 
Such was the case with the release of the new article on headwater streams serving as climate refuges for coldwater fishes. A top-flight group of fisheries scientist recently reviewed a large set of existing stream temperature data from the Northwest and found, to their surprise, that streams were warming at a much slower rate than nearby air temperatures or their models predicted. Over the period from 1968-2011, air temperatures in the Pacific Northwest rose about 0.2°C per decade but actual stream temperatures increased about half that much. We are talking about the smaller, higher elevation streams typically found on national forest or other public lands.That is big news for species like bull trout or cutthroat trout that depend on high quality mountain habitats.
 
We don’t get much positive climate change news these days, so take a moment to thank our public land managers and the many agency scientists and citizen scientists out there collecting badly needed data on stream temperature.
 
But – and there always is a ‘but’ these days – the authors correctly noted that increased temperatures are only one part of the climate change story, and they admittedly did not consider the increased risk to trout populations caused by more extreme drought or wildfires that are encouraged by a rapidly changing climate. In much of the West, and especially in the Southwest that is outside the scope of this study, trout populations are isolated in the highest headwater streams, pushed up the mountains by non-native fishes in the downstream areas and permanently ‘protected’ by constructed barriers meant to keep the non-natives downstream.  
 
 
Water temperatures are only one of the factors of climate change we must be concerned about. Wildfires, like the Whitewater-Baldy fire in southern New Mexico in 2012, wiped out several populations of threatened Gila trout. 
 
Large wildfires and persistent drought are likely to become major drivers in the future survival of western trout populations. In 2012 we watched as the Whitewater-Baldy Fire, which became the largest wildfire in New Mexico history, swept through remaining Gila trout populations, eliminating badly needed populations of this threatened species. Elsewhere, we witnessed the loss of trout populations from drought.  
 
The ability of trout to maintain their populations in a rapidly changing world is the product of many factors that often work in synergy against trout survival. Warming air temperatures, for instance, result in greater evaporation rates and earlier forest drying that promotes landscape-scale wildfires.  
 
Stream temperature is a big part of the equation but not the only climate-related factor out there to contend with. But, we will take good news where we can find it. As the study suggests, we appear to have bought some badly needed time—time to help repair our watersheds and restore our riparian habitats as our planet warms.
  
These days, our trout populations need all the good news they can find. 
 
Jack Williams is TU’s Senior Scientist. He is based in Medford, Ore. 
 
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