| Fish passage
RESTRICTED FISH PASSAGE AT dams is being used to help limit the spread of invasive fish species in the US. Research undertaken by the US Fish and Wildlife Service, US Geological Survey, and Department of Natural Resources has investigated how dams in the Upper Mississippi River (UMR) not only affect the large- scale migration of native fish, but those of invasive species too. Increasing the understanding of how fish move
through lock and dam structures is critical for developing deterrent strategies that effectively limit the spread of aquatic invasive species while protecting migration corridors for native fish.
A series of 29 navigation locks and dams across the UMR basin has led to a high degree of channel fragmentation that impacts fish migration, with fish passage through dams being influenced by the design features of individual structures. To give greater insight into this, a two-year study tracked the native American paddlefish and invasive bigheaded carp across more than 600 river kilometres and 16 navigation locks and dams (LD) of the UMR. As a variety of socioecological problems are associated with increasing invasive bigheaded carp populations, such as safety hazards for boaters to food web disruptions, it is considered necessary to prevent further upstream spread. As detailed in the research, LD 19 has a
hydroelectric facility and the highest vertical lift of the active navigation locks on the UMR. It also has a hydraulic head that is too great to permit fish passage through the gated portion of the dam. And with LD 15 and LD 14 infrequently in open-river conditions, such restrictions on upstream passage at LD 19 and LD 15 have played a large role in reducing the population of invasive carp upstream, and is why the portion of the UMR between LD 19 and 15 is seen as a focal point for invasive carp control. In their research published in Scientific Reports, Fritts et al say that in order to effectively balance the trade-offs between reducing invasive carp passage and facilitating the passage of native species, information is needed on how fish passage is affected
www.waterpowermagazine.com | March 2025 | 25
by dam operations and other influential factors, such as temperature. Indeed climate change is likely to have more of an influence on fish movement, and may result in such changes to the timing of seasonal food pulses. The purpose of this study was to examine movements of paddlefish and bigheaded carp with respect to dams and the abiotic factors affecting both dam operations and fish physiology. The researchers used consecutive years with contrasting conditions to explore how fish responses changed as conditions varied between 2022, a low-water year, and 2023, and a high-water year. As the authors explained, large-scale comparison of native and invasive fish passage is an important step to facilitate a stronger understanding of how climatic variables such as precipitation and warming temperatures affect the abilities of native and invasive species to traverse the existing infrastructure of the UMR. The results highlighted that dam operations during controlled hydrologic conditions can limit upstream passage. Conversely, during uncontrolled hydrologic conditions, when the dams allowed for open-river conditions, fish moved rapidly upstream. Characterising the magnitude and relative
Above: Lock and Dam 15 on the Mississippi River in Illinois, US
Below: American paddlefish
Below: The Chief Joseph Dam on the Columbia River
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