Making fish comfortable at road crossings
Why did the salmon cross the road?
It may sound like a setup to a bad joke, but University of Alaska Fairbanks researchers Charles Behlke and Douglas Kane spent more than a decade pondering that question. In the early 1980s, the UAF engineering professors began an in-depth look at how grayling and juvenile salmon navigated road culverts.
It's an important question, because a poorly installed culvert can cut off important habitat and spawning grounds. With help from the Alaska Department of Fish and Game and Alaska Department of Transportation and Public Facilities, Behlke and Kane studied sites in Southcentral and Southeastern Alaska to figure out how fish handled those manmade passageways.
They used underwater video cameras to see how fish traveled. They tagged or marked grayling and salmon to see where they went, and put white sheets of plywood on creek bottoms so their activity was more visible.
According to conventional wisdom, fish were unwilling to use a culvert that presented even a mild challenge. But Behlke and Kane found that their subjects could overcome significant obstacles as long as the rewards of food or spawning opportunities were waiting at their destinations.
"We learned that fish could do a whole lot more than people thought they could when they were motivated," Kane said.
Their study, published in 1994, recommended some ways to install more fish-friendly road designs. They also determined that culverts could be suitable road crossings in many places instead of more expensive bridges, a finding that had big implications for Alaska road budgets.