UBC Theses and Dissertations

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UBC Theses and Dissertations

Determining the effects of sediment deposition on the growth, survival, and foraging efficiency of the endangered Nooksack dace (Rhinichthys cataractae sp. cataractae), and on the abundance, distribution, and community structure of their invertebrate prey. Champion, John Michael


Alterations to riverine habitats from the excessive deposition of sediments present a challenge for the effective management and conservation of aquatic resources and endangered species. The Nooksack dace (Rhinichthys cataractae sp. cataractae) is an endangered, benthic riffle-dwelling specialist, which is threatened by sediment-induced habitat changes. The purpose of my thesis was twofold. First, using semi-natural streamside channels I experimentally tested how different levels of embeddedness and percentages of fine sediments <2 mm in diameter affected the biomass of benthic invertebrates and the growth of Nooksack dace. Second, using artificial foraging arenas I manipulated substrate characteristics (i.e., embeddedness) and water velocity to examine how they jointly affected the foraging efficiency of Nooksack dace. Goals were to use these complementary approaches to distinguish between reduced invertebrate prey abundance vs. physical impacts on foraging efficiency as mechanisms mediating sediment effects on Nooksack dace growth. My results showed that invertebrate biomass generally decreased as embeddedness increased and that mortality through predation on Nooksack dace was highest over partially and fully embedded substrates. My findings also suggest that the loss of interstitial space had a more significant effect on invertebrate biomass and Nooksack dace survival than the percentage of fine sediments. However, the presence of fine sediments exacerbated the negative effects of embeddedness, especially for burrowing invertebrates. I also found that Nooksack dace foraging efficiency decreased over all substrate types as water velocity increased. This suggests that although Nooksack dace are associated with unembedded gravels in high velocity riffle habitats, they are likely adapted to foraging in low-velocity micro-habitats within the boundary layer. Sediment-induced habitat changes resulting in high near-bed water velocities likely have a negative impact on Nooksack dace foraging efficiency, which in turn could negatively affect their growth and survival.

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