Life history and bioenergetic modelling of adfluvial-lacustrine coastal cutthroat trout predation in the Capilano Reservoir : implications for endangered steelhead, coho salmon and future holistic watershed management strategies

Abstract

Coastal cutthroat trout (Oncorhynchus clarkii clarkii) are the apex predator in the Capilano Reservoir. This thesis investigates cutthroat predation via bioenergetic modelling and demography, and genetic analysis of hybridization with coastal rainbow / steelhead trout (O. mykiss irideus). The bioenergetics model, based on stomach content analyses, reservoir temperature and growth rates, in conjunction with predator abundance, estimates that adult trout in the reservoir consumed 6.4% of coho (O. kisutch) smolt production in 2010. No evidence of cutthroat predation on juvenile steelhead out-migrants was detected, and a gape prey maximum of 36% of predator body length was found. Moderate hybridization rates between cutthroat and rainbow trout were detected, as well as previously unknown pure strains of adult rainbow trout in reservoir waters, indicating reservoir residualization. Cutthroat trout are currently a 'second tier' management species in the Capilano Watershed, and greater understanding and appreciation of their adfluvial-lacustrine life history will facilitate informed decision-making for trout conservation and restoration, and coho management in the reservoir and the Capilano Watershed.