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UBC Theses and Dissertations

Habitat fragmentation in the Fraser River watershed : implications for salmonid habitat remediation and management Zubick, Patrick


Habitat fragmentation has been implicated in broad declines of Pacific salmon and trout populations in the Pacific Northwest of North America. Dams are often considered to be the largest driver of fragmentation. However, small-scale barriers like floodgates, weirs and culverts can have significant negative impacts on stream habitat. In British Columbia (BC), Canada, an estimated 135,000 - 200,000 culverts act as barriers to fish passage, making them a major issue for salmonids and a target for restoration. Despite barrier culverts being one of the leading anthropogenic causes of stream fragmentation globally and a frequent target of restoration efforts, the efficacy of these interventions and their conformance with best practices has rarely been examined. Effective planning of these restoration efforts is often hindered by incomplete barrier inventories and uncertainty about where best to perform restoration. I addressed these issues by performing two complementary studies. I first performed a 'post-treatment' audit of culvert barrier remediations in southcentral BC through an examination of current physical attributes at 15 retrofit and 15 replacement sites and scored sites based on the BC culvert fish passage assessment and on best practice guidelines for stream crossings in BC. I then used two modelling approaches to evaluate historical habitat availability, how barriers potentially prevent Chinook and Coho salmon migrations, and the role of barrier remediation in enhancing habitat accessibility in the South Thompson watershed of BC. At barrier remediation sites, 80% of retrofits and 20% of replacements were classified as fish passage barriers, and conformance with best practices was at most 80% at any site. I modelled that Chinook and Coho salmon historically had access to 3600 km and 3400 km of stream length, and these habitats are currently impacted by 1955 barriers. These results show that fragmentation of salmon habitat is a widespread issue, potentially exacerbated by predicted barriers, and that poor conformance may be hindering the effectiveness of remediation actions.

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