Methodology for Assessing and Evaluating Waterfall Fish Passage Barriers in Alberta
Invasive species are potentially the greatest threat to westslope cutthroat trout (WSCT) in Alberta, through hybridization, competition, and displacement. To effectively safeguard against extirpation, it is essential that existing pure populations of WSCT remain protected from invasive species, and additional populations are established outside of areas that WSCT currently occupy. Several sub-populations of WSCT remain genetically pure because of waterfall barriers that impede upstream migration of invasive fish. Similarly, habitats above barriers that are currently unoccupied by WSCT represent opportunities to expand their range and total habitat area through introduction/re-introduction of pure stocks. Before re-introductions can begin, identification and broadscale inventory of barriers that isolate WSCT populations and habitats is a crucial priority to build range expansion strategies on a stream-by-stream basis. To date there is no single assessment method to identify and rank barrier passibility in the context of invasion risk. Our objective was to develop a standard method for barrier assessment. In 2017, we began modifying methods to assess the ability of trout to successfully ascend barriers based on documented research of their swimming and leaping capabilities. By the summer of 2018, we had evaluated approximately100 known barrier locations containing approximately 200 barrier features, and developed a four-tiered classification system to catalogue a complex array of different barriers. We assessed barrier passibility based on the leaping and swimming ability of various sized trout, and severity of white-water turbulence. We developed a system to score barriers. A final list of scored barriers will rank the potential for each barrier to successfully protect introduced WSCT populations from invasive species downstream. This list will ultimately be used in a related scoring framework that ranks and catalogues habitats above barriers by range expansion potential and feasibility, from which agencies can select individual habitats on which to focus re-introduction efforts.
Alberta Environment and Parks
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