Use of Mussel Spat Rope for Fish Passage in Culverts

Culverts can act as barriers to fish and aquatic organism passage by a number of mechanisms including insufficient water depth or excess velocity, perched culvert outlets, excess turbulence or behavioral barriers. In Minnesota, maintaining unimpeded fish passage is a concern due to our high-quality fisheries; however, much of the fish passage research in the United States has been conducted on the coasts with anadromous species. Many different methods have been used in Minnesota and nationally to facilitate passage including retrofitting existing culverts. In larger culverts, methods such as baffles or weirs have been installed to create resting areas for fish in culverts with high velocities, but these can be costly, difficult to install in tight culverts, can create maintenance issues, and may only be applicable to larger fish species. Recent research from New Zealand demonstrated the effectiveness of mussel spat rope in facilitating fish passage in steep, perched, or high-velocity culverts. The installation of these ropes in Minnesota box culverts was investigated as a low-cost, low-maintenance method to facilitate fish passage, specifically focusing on 1) the hydrodynamic performance of the ropes, 2) the use of these ropes by Minnesota fish species, and 3) evaluation of field installations in typical box culverts. This project used a combination of physical laboratory measurements on rope hydrodynamics, fish laboratory experiments on use of ropes, and two field demonstration sites. Ropes created low-velocity areas and cover that were utilized by small fish to navigate shallow flows over smooth boundaries.