Barriers to fish passage and barriers to fish passage assessments: the udimpact of assessment methods and assumptions on barrier identification and udquantification of watershed connectivity

摘要

Barriers (culverts and dams) can impede fish passage and affect the overall habitat connectivity of rivers. udHowever, a challenge lies in how to conceptualize and adequately measure passability at barriers. We udhypothesize that estimates of barrier and watershed connectivity are dependent on assumptions about theudnature of passability, and how it is measured. Specifically, we compare passability estimates in TerraudNova National Park, Canada for individual barriers for two barrier assessment methods (a rapid udassessment, and one based on FishXing software), two salmonid species, different fish sizes and udswimming speeds, and varying hydrological conditions. Watershed connectivity was calculated using the udDendritic Connectivity Index (DCI). Lastly, we test to see what the impact of the various factors is on the udpractical goal: prioritizing barriers for restoration. Our results show that barrier passability estimates can udvary drastically for some barriers (0-100%). In general, the rapid field-based assessment tended to give udmore conservative estimates of passability than those based on FishXing. Estimates of watershed udconnectivity were not as sensitive to the assumptions and methods used (DCI: 40-83). Fish size had the udgreatest effect on DCI. Importantly, variation in DCI had little impact on the restoration priorities. The udsame barrier was retained as the top priority >96% of the time. Thus, managers wishing to assess barriers udfor restoration need to carefully consider how passability is to be measured, but can reduce the impact of udthese decision by considering barriers in their watershed context by using a connectivity index such as the udDCI.