Fish behavior guides riverbank repairs
April 9, 2013
The banks of the Sacramento River experience constant erosion and that's a big reason why Sacramento has some of the highest flood risk in the nation. It's also the reason the U.S. Army Corps of Engineers Sacramento District conducts an annual survey of the Sacramento River and its tributaries to determine where the worst erosion is taking place and which erosion sites should be repaired first.
While reducing flood risk is a significant mission for the Corps, it's equally important to ensure that work helps restore and preserve wildlife habitats for five threatened or endangered fish species that travel down the Sacramento River.
Reducing flood risk in an environmentally mindful way is what brought ecologists to the Coleman National Fish Hatchery in Anderson, Calif., March 25-27, 2013 to surgically implant electronic tracking devices into hundreds of live fish to study their behavior.
"We're always looking for ways to make our projects more environmentally friendly," said Natalie Houghton environmental specialist with the district. "To do that, we need to determine how our constructed habitat features are impacting fish and really look at how they're reacting to our repair sites, compared to other areas of the river."
Knowing exactly where the 1-year-old juvenile steelhead trout and Chinook salmon are, and studying how each and every one responds to riverbank repair sites, offers insight for improving the district's efforts to restore the native species' environment, while reducing continuing to reduce flood risk.
"The idea is that we are creating habitat for the fish, so we want to know if the fish are actually using those sites or if there are other things we can do to make those sites more beneficial to salmonids," Houghton said. "Our process is to first place the fish in a numbing agent, to make sure they don't feel anything. Then, we create a small slit on the bottom of the fish, surgically implant a tracking device and then suture it closed. Then we place the fish into a recovery tank overnight and release them the next day."
Once released, more than 100 acoustic receivers throughout a 75-mile stretch of the Sacramento River will pinpoint the location and identity of individual fish, and record how the fish are moving through the system.
Dave Smith, a research ecologist for the Corps, has spent the last two years inputting fish-tag data into a computer model developed by the Corps' Engineer Research and Development Center in Vicksburg, Miss. The model helps evaluate habitat restoration work and provides environmental benefit information to projects for the Corps and other agencies.
"Our goal is to essentially provide rearing habitat along the levee corridors," Smith said. "We know the fish are responding to the features we've built on the levees, so, we're trying to tease out exactly what it is they are responding to and hopefully turn that back into design guidance for improvements to habitat features."
Preliminary results from the fish-tag data are encouraging.
"It's still very early, but we're noticing good results so far," said Houghton. "Based on preliminary analyses, they seem to be migrating down the river just as they would under natural conditions."