Passages built beside dams to allow trout and salmon to continue moving upstream are common mitigation tools but do these structures work for little fishes too? In a new study published in Canadian Journal of Fisheries and Aquatic Sciences researchers from Kansas State University track the movement of smaller-bodied fishes (<100 mm in length) up and over a dam.
From Montana down to Texas and Colorado across to Missouri, rivers in the American Great Plains formed roughly 5–23 million years ago. Rivers are of value not only to citizens of these regions but also the flora and fauna that inhabit them. Fishes that live in the Great Plains rivers have evolved reproductive strategies allowing them to thrive in these rapidly changing systems that due to the harsh climate of the region experience tremendous natural variation in flows across seasons and years. One group, the pelagic-spawning minnows, disperses their fertilized eggs and larvae during seasonal high-flow events. These fish rely on the ability to migrate upstream to both spawn and recolonize newly wetted stretches of river.
But for minnows migrating in the Arkansas River as it moves through the City of Wichita, Kansas, their egg-dispersing efforts hit a wall: the Lincoln Street Dam.
Science in the city
Wichita’s Lincoln Street Bridge was first built in 1970 and included an inflatable dam attached below the bridge (see some examples of inflatable dams). The explicit purpose for the inflatable dam was to beautify the Arkansas River by backing up the water as it passed through downtown portions of the city to create a lake-like appearance. A permanent concrete structure replaced the inflatable dam in 1976. Construction began in 2010 to replace both the bridge and dam because of structural deficiencies. The new bridge and dam were built separately and a passage was constructed for kayaks and canoes. On each side of the passage are fishways: structures used to allow migration of fish over or around dams that would otherwise block upstream movement.
The Lincoln Street Fishway follows a pool–orifice design, which is a series of pools separated by steel plates each with a window fish must swim through and has been in operation since 2015. Most fishways are built on high gradient, rocky streams inhabited by large, migratory fish species like salmon and trout. The Lincoln Street Fishway is unique because it was built on a gently sloping sand-bed river and targets the passage of small-bodied minnows. Because fishways on this type of river have not been studied extensively, the construction of this structure presented an opportunity to measure its effectiveness at restoring access to upstream habitats (i.e., above the dam) for an entire fish community.