Fishways, Fragmentation, and Imperiled Great Plains Fishes
October 5, 2017
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.
By Casey Pennock
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 cityWichita’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.
|Aerial view of the Lincoln Street Bridge, Dam, and Fishway (Richard Schultheis)|
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.
|To assess the impacts of the fishway on the fish communities upstream and downstream of the dam, we conducted multi-year, multi-season sampling of sites upstream and downstream of the fishway and simultaneously sampled the entire fishway. This required a lot of effort by my field crews and we spent many hours in the field identifying, measuring, and counting over 160,000 individual fish. We also conducted several experiments where we tagged (with an internal electronic tag) or marked (with injectable paint) just over 21,000 fish to characterize how they moved into and through the fishway. By comparing results from our sampling effort of the upstream and downstream communities to sampling conducted by the City of Wichita prior to the fishway being constructed, we were able to identify changes in the fish communities resulting from the construction of the fishway.
|Seining and counting thousands of fishes was the name of the game throughout much of the project (Jessica Mounts)|
Because our research was conducted in an urban area, we were presented with some unique opportunities and challenges. The most prevalent is that eyes are always upon you and people are curious about what you are doing. Luckily, most of our encounters with citizens of Wichita were largely positive and we were able to explain our research efforts to an eager-to-learn crowd. Research conducted in urban centers provides an educational platform for scientific investigations and the conservation issues these fish are faced with because it is happening right in people’s backyard. This study was a great opportunity to showcase our work and results to an interested audience of concerned citizens in real-time.
Upward and onward, but for how far?Our research shows that the construction of the Lincoln Street Fishway has allowed for movement of many species of fish into upstream habitats that otherwise would have been blocked by the dam. Prior to the construction of the fishway, species richness (the number of species) was lower upstream of the dam and community structure (the number of species and their relative abundances) was noticeably different among downstream and upstream reaches.
|Sand shiner were one of three minnow species tagged and tracked (Ellen Edmonson/Hugh Chrisp, Public Domain)|
Species previously eliminated from the upstream reach following dam construction, such as the emerald shiner, can now be found above the dam and there is more overlap in community structure upstream and downstream of the dam. However, for some species, differences remain in the size of fish collected upstream versus downstream of the dam: fish above the dam are bigger than fish below. This could mean that smaller fish have a more difficult time moving upstream through the fishway, or it could mean that larger, sexually mature fish are more mobile or driven to move upstream than their younger counterparts.
While the fishway has allowed for improved continuity of the Arkansas River fish community, changes to habitat caused by the dam remain. A potential problem with fishways is they provide the opportunity for, and may even entice, fish to move upstream even though habitat deficiencies above the dam cannot support viable populations. This has led some researchers to refer to fishways as "half-way technologies". For example, the Lincoln Street Dam impounds the river upstream for 3 km, creating a lake-like habitat in which we found lowered diversity and fewer fishes overall relative to flowing portions of the river below the dam and beyond the impoundment.
|The Lincoln Street Dam impounds the Arkansas River for 3 km upstream creating a lake-like habitat (Casey Pennock)|
This lake-like habitat might be a problem for fishes that have successfully ascended the fishway. They may be more easily eaten by predatory fishes as our study found the impounded reach of the river had the highest number of predatory fishes (e.g., largemouth bass, green sunfish, and flathead catfish). Another dam exists 9 km upstream that likely keeps fish from moving any further upstream. Pelagic-spawning minnows could potentially pass the fishway and spawn upstream, but eggs and larvae would likely drift into the impounded water. If the fishes spawn in the impounded water or eggs and larvae drift, survival could be compromised by increased predation or because lack of flow causes eggs and larvae to fall out of suspension where they could suffocate in the sediment.
Despite these potential shortcomings, our study suggests that fishways provide improved continuity for fish communities of sand-bed rivers. In the Great Plains, pelagic-spawning minnows rely on connectivity and seasonal flow variation to complete their unique reproductive strategy. Dam construction is widespread across the region for everything from urban beautification projects to large-scale water storage. But the potential for fishways to ease the effects of fragmentation on fishes in the Great Plains is high. Restoration and maintenance of adequate riverine habitat is desperately needed to ensure the long-term persistence of endemic Great Plains fishes.
The article entitled "Can Fishways Mitigate Fragmentation Effects on Great Plains Fish Communities?" is available on the NRC Research Press website.
Header image by the author, Casey Pennock.
|Casey Pennock is a PhD graduate student in the Division of Biology at Kansas State University researching early life-history and movement behaviours of razorback sucker in the American Southwest. He obtained his MSc at Kansas State University. His MSc thesis project, completed with the help of his colleagues, was the focus of this CJFAS paper. Find Casey on Twitter or check out his website.|