Effectiveness monitoring of culvert and floodgate remediations to improve salmon access to critical freshwater habitats

Culverts and floodgates have created a large, and poorly quantified, network of barriers to fish movement, with the strongest impact being felt by obligatory migrators such as potadromous and anadromous salmonids. Pacific salmon (Oncorhynchus spp) cannot access thousands of kilometers of spawning and rearing habitat because of this issue. To address this pervasive form of freshwater habitat fragmentation, work has been done to remediate barrier sites and reopen otherwise viable stream and floodplain habitats. However, little monitoring has been done to assess the effectiveness and longevity of these remediations for improving salmon habitat access. My dissertation builds off the growing body of literature exposing the impacts of small-scale barriers on Pacific salmon recovery and assessing the effectiveness of various barrier mitigation measures. I describe how we designed and deployed novel noise-canceling PIT (passive integrated transponder) antenna designs to more accurately track juvenile salmon movements through areas of high electromagnetic interference such as occurs at floodgates and culverts. I also report results of an intensive PIT telemetry study tracking juvenile coho salmon (O. kistuch) movements through floodgates in the lower Fraser River. I found that a self-regulating floodgate, which is designed to remain open for longer on an incoming tide, drastically improved juvenile salmon access to overwinter floodplain habitat compared to a traditional top-mounted floodgate. However, in a year of high winter mainstem flows, juvenile salmon passage was severely hampered through all floodgate sites, whereas passage through an ungated reference site remained unchanged, suggesting that ungated off-channel floodplain habitats may be important refuge sites under future climate scenarios. I also report on an extensive large spatial scale study exploring the efficacy of different culvert remediation approaches in restoring passage for anadromous and resident fish. These results provide strong support that culvert retrofit remediations that do not remove the culvert created barriers to passage for a range of species whereas culvert replacement with bridges in general appeared to provide passable environments. I conclude the thesis with a discussion of the current policy and management challenges limiting floodgate and culvert barrier remediation or removal and I propose recommendations to improve salmon habitat connectivity.