Small mouth, big appetite: diet analysis of invasive smallmouth bass (Micropterus dolomieu) in Cultus Lake, British Columbia

As aquatic invasive species spread, their impacts on native systems are variable and important to understand from a management perspective. DNA sequencing and morphological analysis of stomach contents can provide insight into the diet of invasive opportunistic feeders, such as smallmouth bass (Micropterus dolomieu). Since their illegal introduction in 2017, smallmouth bass have proliferated in Cultus Lake, British Columbia and potential impacts on two species-at-risk (sockeye salmon and pygmy sculpin) are currently unknown. Bass (n = 204) were sampled in the spring/summer of 2020–2021 in Cultus Lake. DNA barcoding (n = 145) and visual analysis (n = 204) of diet were completed. Diet composition, factors influencing the predation of species-at-risk, and dietary shifts were analyzed. DNA analysis identified 32 more taxa at the family level than morphological analysis. Multiple logistic regression showed that bass were more likely to predate on Oncorhynchus nerka within the bass spawning grounds, and over 90% of bass had sculpin in their diets. Diet composition did not shift as bass size changed, demonstrating sustained predation on fish from 100 to > 300 mm total length. These results highlight the importance of understanding the potential impacts of an invasive species before investing in suppression to create effective plans and leverage funding opportunities.