Michelle Gros

McGill University
Yellow perch responses to winter drawdown in North temperate reservoirs: Insights from stable isotope and morphometric approaches

Gros, M. , Turgeon, K.  Finney, B.  & Gregory-Eaves, I.

Winter drawdown is a common management practice in reservoirs across temperate regions of the globe. Drawdown exposes littoral shorelines, modifying ecosystem attributes that are critical to the survival of biota. Physical characteristics of these littoral environments are modified with drawdown, which alters the quality of the habitat and potentially affects whole reservoir ecosystem functioning. Changes in the littoral zone may cause some fish to forage more heavily in the pelagic zone of the reservoir, alter their feeding behaviours, and shift their habitat coupling patterns. To address these issues, we investigated the effects of winter drawdown on yellow perch (Perca flavenscens) trophic responses across the littoral-pelagic axis by using carbon and nitrogen stable isotopes and morphometric data. Yellow perch and food web end-members were sampled from six reservoirs along a drawdown gradient. Using Bayesian inference isotope mixing models, we identified that perch diets from low drawdown reservoirs rely more heavily on benthic sources compared to fish from high drawdown reservoirs that rely more on low quality pelagic sources. Morphometrics analyses also revealed that perch have a more streamlined body shape in the low structure, high drawdown environments. Finally, we mapped perch shape and diet into 2D space in order to determine differences in behavioural and niche diversity across different drawdown regimes. Our findings suggest that drawdown can have serious implications for perch population health and may extend to whole ecosystem due to the high mobility of this predator and the top-down control it may have on lower trophic levels.