By Deborah Holt Williams
When it comes to surviving a forest fire, fish might seem like the lucky ones. After all, their habitat can’t burn, right? Unfortunately, fish suffer, too—after the fire is over.
Trees, shrubs and other plants keep the soil in place with their root systems. But when these roots are burned, there’s nothing to hold on to the dirt, and the first rain sends a load of soil and ash into the rivers and streams.
This sudden dump of dirt makes the streams shallower, and more easily warmed by the sun. The combination of warmer temperatures and more sediment can make the water more acidic. The ashy mess also makes the water darker and murkier, and harder for river plants to make energy from the sun through photosynthesis. None of this is good news for the fish.
But there’s more. Bob Parmenter of the Valle Caldera Science and Education Center in Jemez Springs, N.M., notes that normally, the amount of ammonia in the water is kept in check by bacteria. But when these bacteria are killed in the fire, the ammonia level increases, and fish are often killed.
And it gets worse. Tony Jacobson, director of the Seven Springs Fish Hatchery north of Jemez Springs explains: “High sediment loads may impact the oxygen level in the water, irritate the fish’s gills and overwhelm the fish’s respiratory system to the point where they can no longer get the needed oxygen from the water.”
After the massive Las Conchas wildfire near Jemez Springs in the summer of 2011, the hatchery stopped stocking the river with trout. They were able to stock in the winter, when freezing temperatures prevented the runoff. The spring thaw turned the Jemez River black, and stocking will have to wait until the water is safe.
Shallower rivers, warmer water, more ammonia, less oxygen, fewer water plants, and irritated gills are all the effects of a forest fire’s aftermath. Some animals may be able to escape the fire and run or fly to unburned areas, but fish are trapped.
Although fish habitat doesn’t burn, it becomes so badly damaged that many fish cannot survive. But nature recovers with time. Gradually, the runoff ends, the water quality returns, and the fish will once again thrive in rivers and streams.