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Climate Change Adds More Stress to Struggling Fish Populations

By Stephanie Paige Ogburn, E&E reporter
9/5/2013 11:48:02 AM

Last summer, anglers visiting Yellowstone National Park may have been disappointed to find a favorite fishing spot closed. Due to high temperatures and low rainfall, parts of the Madison, Gibbons and Firehole rivers were closed to fishing in August 2012.

It wasn't just fishermen who lost out. Freshwater fishing makes big money for local economies: In 2011, spending on the sport totaled nearly $26 billion, and in rural economies, the money spent by tourists on guides and gear can be a significant boost.

The future is likely to hold more closures of the type seen in Yellowstone as stresses on freshwater fish increase due to climate change, according to a report released yesterday by the National Wildlife Federation.

"Studies of river and stream temperatures show warming trends in half or more of the places where we have long-term data sets," said Amanda Staudt, a climate scientist with the National Wildlife Federation. "This warming has direct effects on fish, especially in summer, when temperatures can exceed what fish can tolerate."

According to Trout Unlimited fisheries scientist Jack Williams, who also co-authored the report, trout and salmon, which rely on cold-water streams, are hugely affected by climate change.

"A lot of the problems that salmon are already facing are kind of made worse by climate change," Williams said.

In much of the western United States, salmon have seen their habitat disrupted by dams that block rivers or erosion that silts up streams and carries pollutants into their habitat.

Photo by: Flickr user Mike Miley

Wildfires add silt; snowmelt comes early

Climate change adds another layer of difficulty. As wildfire seasons lengthen and fires become more severe, runoff from burned areas could add even more silt into streams. Earlier snowmelt, another likely outcome of a warming world, can also hurt fish.

"Normally, when we have a good snowpack, the waters will slowly melt off and it will kind of percolate down into the stream so that we have greater base flows into the summer," Williams said.

But if snow melts too early, stream flows can get very low late in the season, and fish can die or fail to reproduce if that happens.

In the desert Southwest, some species of threatened fish, like the Apache trout, already exist in very limited parts of streams. When wildfire comes through, the severe runoff after the fire can dramatically affect fish populations, with such limited habitat.

"One of the problems that we have with these extreme forest fires was, for example, the excessive runoff that occurred [after the High Park fire] in Colorado," said Doug Inkley, a senior scientist with the National Wildlife Federation. "It actually turned the Poudre River black with ash, which is obviously bad for fish."

One solution to this problem, the report authors say, is to expand high-quality habitat for fish so they can move out of areas heavily affected after a fire. One way to do this is to restore the areas along creeks and rivers with plants that can offer cooling shade and filter sediment.

Invasive species flourish

Invasive species are also likely to respond in new ways to climate change, especially as water temperatures change, allowing some species to thrive at the expense of others. In the Great Lakes region alone, invasive species create costs of about $200 million yearly, according to the report.

One invasive Great Lakes fish, the sea lamprey, is expected to benefit from higher temperatures. It grows larger and reproduces better in warmer waters, meaning its population could increase and it could pose more problems for native fish in the region.

Warmer winters are also likely to change sport fishing. Ice fishing, a popular pastime in the Midwest and Northeast, has lost 18 days in its season over the past 150 years due to rising winter temperatures.

Those parts of the country are also experiencing winter warming above average; temperatures in the Midwest and Northeast have warmed by 3 to 4 degrees Fahrenheit since 1970, said the National Wildlife Federation's Staudt.

Other changes in northeastern weather include the number of flood events. Various parts of New England have experienced "hundred year" storms for multiple years in the recent past. Recent attempts there to implement flood control by channelizing rivers can actually hurt fish by removing boulders and trees, key parts of their habitat, said Trout Unlimited's Williams.

In order to better prepare for future floods without hurting fish, managers need to plan to restore wetlands and floodplains, which can act as a natural flood control.

"A lot of that depends on early planning and early discussions rather than waiting for a big storm to hit and then everybody declaring an emergency and then anything goes," Williams said.

Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. 202-628-6500.

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