Sunday, September 2, 2012

Our Hot and Dirty Rivers

Salmon. That single word evokes strong images and feelings in so many of us. Indeed, it was the single most memorable word from Obama’s 2011State of the Union address. Depending on your perspective, salmon can be your livelihood, a necessary thread for the health of the ecosystem, a vital part of your cultural heritage… or of course, purely delicious. And despite, or perhaps because of, their importance, their populations are at a fraction of what they were half a century ago. Many factors are contributing to their decline, including impacts from dams, habitat loss, reduced flows due to irrigation, toxic algal blooms, disease, and fishing pressures.

So what can we do to restore our salmon populations? Because salmon have a life cycle that spans both rivers and ocean, the answer is not simple. Salmon are anadromous, meaning that juvenile salmon spend as much as 1-3 years in rivers before heading to the ocean, making the health of our rivers extremely important for their survival. Water temperatures are rising in many rivers along the west coast, and since salmon are a coldwater species and ectotherms (their body temperature changes to match their environment), these elevated temperatures are extremely stressful for them. Imagine a 110°F day without air-conditioning… then imagine that your body temperature rose to match the outdoor temperature. We might be moving to a different part of the country pretty quickly if we were ectotherms. Hot water temperatures, along with bad water quality, are just some of the hurdles that young salmon face on their journey to the ocean.

I study juvenile steelhead on the Klamath River in northern California. I am interested in how habitat constraints (temperature, food) affect steelhead behavior, growth and survival. On summer mornings, the Klamath River actually steams; the water can reach 80°F, and feels like a lot like bathwater. The hot river temperatures cause juvenile steelhead to move into coolwater refugia created by incoming creeks. They pack into these areas—there can be up to 400 fish in one small pool—raising questions about how much refugia area is necessary for them to survive the summer months. I study the dynamics of these refugia, and do radio tagging studies to determine how food availability and water temperature are affecting their behavior.


  1. How large are the refugia? What is the temperature difference between the refugia and the river? Can you really see
    the fish packed in the refugia? lvb

    1. They vary in size, depending on the size of the incoming tributary. But they can be as large as ~100m long and half as wide as the river (~30m). The temperature difference also depends on the incoming tributary, which is usually about 6-8C cooler than the river, creating a huge thermal gradient. And yes, you can see tons of fish packed in there, if you just grab a mask and stick your head in!