Abstract
Rainbow Smelt Osmerus mordax are the primary coldwater forage species in Lake Oahe, South Dakota, yet most aspects of their life history remain unknown. As Missouri River reservoirs present a novel habitat compared to elsewhere in the Rainbow Smelt’s range, we investigated their spawning site use relative to available physical and thermal habitat from spring 2016 − 2018 using a mobile horizontal-beaming hydroacoustic survey. We mapped spawning habitat using side-scanning sonar to establish relationships with site bathymetry and thermal spawning conditions. From our site mapping, we determined the depth, slope, bottom hardness, and ruggedness of individual sites. We used a PCA to condense our physical habitat metrics, with PC1 representing 77% of cumulative variance. Peak abundance was linked to a physical habitat gradient, representing [steep slope, deep, soft bottom] to [low slope, shallow, hard bottom]. Peak Rainbow Smelt spawning aggregations were observed at 6.8 ± 1.7 °C (Mean ± StDev). An information-theoretic regression analysis revealed an interactive effect of temperature and habitat, whereby shallower, warmer sites typically had a lower peak abundance. These results represent the first step toward understanding habitat use characteristics of spawning Rainbow Smelt in reservoir systems.
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