Fish Passage Through Retrofitted Culverts PDF Download

The improper design, installation, or maintenance of culverts has the potential to create barriers in aquatic systems, which in turn may lead to fish population declines. Culverts identified as having fish passage issues, e.g., perched or sized incorrectly, are often retrofitted with fish passage structures, i.e., fish ladder or chute, as a cheaper alternative to replacement. The purpose of this research was to evaluate the effectiveness of culvert retrofit designs for fish passage commonly used in New Brunswick. Ten culvert sites across New Brunswick, 7 of which were retrofitted with pool and weir fish ladders and 3 with chutes, were chosen for this study. Each site was outfitted with radio frequency identification (RFID) reader and antennae, which were situated to assess entrance and passage of fish through the fishway and culvert. Fish that were electrofished downstream of the fishways were surgically implanted with 23mm passive integrated transponder (PIT) tags, then released approximately 100m downstream. During this study, 965 fish were tagged: 10 sites and 6 species. The RFID detection efficiency across sites averaged 57% (range = 25-76%). The fish passage was measured among three structures: the entrances to the fish passage structure, the chutes or pool and weir passage structures, and the culverts. Except for extremely low water conditions, the entrances to the fish passage structures were generally submerged, resulting in high entrance efficiencies, i.e., the proportion of fish that moved into the site and entered the fishway. Passage efficiencies, i.e., proportion of fish that entered the fishway or culvert and successfully passed through, for the pool and weir fish ladders and chutes ranged from 75-100%. The culvert efficiencies were 61-98%, across sites and species. Few differences in physical conditions, i.e., temperature and discharge, or among species sizes were observed between successful and unsuccessful attempts to pass structures and culverts. Often, too few fish passed for complete analyses. Velocities through the weirs and culverts during attempts were within the reported swimming abilities of each species. Overall, the structures passed fish as intended; however, several issues were apparent and often the most important barrier issue was the accumulation of debris in the weir or chute notches and water levels. Fish were not detected passing through the site when debris blocked the weirs or chutes. Likewise, no passage was detected at some sites during periods of very low discharges.