Body condition and diet data for gamefish in 15 hardwater lakes of southern Saskatchewan, Canada

Mitigating threats of aquatic invasive species in lakes requires holistic insights into the biological, physical, and chemical conditions sustaining fish communities. This study establishes the ecological baseline conditions for three key gamefishes—walleye, northern pike, and yellow perch—across 15 hardwater prairie lakes in south-central Saskatchewan, Canada, that are threatened by zebra mussel invasion. We employed stomach content analysis to evaluate diet composition and ontogenetic nutritional shifts in adult fishes and assessed how fish size and environmental factors influence body condition. Adult walleye transition from a diet of amphipods to fishes as they grow, demonstrating greater dietary flexibility compared to perch and pike, which maintain a stable diet of chironomids and fish, respectively. While walleye and pike decline in body condition with size, perch maintain a consistently high body condition as they grow. Lake productivity and alkalinity are important predictors of body conditions of adult walleye and perch in hardwater prairie lakes. Given the combined threats of zebra mussel invasions, climate change, and potential local forage fish scarcity, novel management strategies are essential.

Methods
Fish and water sampling were conducted across 15 hard-water lakes in south-central Saskatchewan from May to August 2019 to establish baseline ecological conditions. Gamefish species (walleye, northern pike, and yellow perch) were measured for length and weight. Stomach content analysis quantified prey contributions using the index of relative importance (IRI). Multivariate analyses (MANOVA, RDA) assessed diet variation between size groups while controlling for lake effects. Multiple regression and relative importance analysis examined how total length and environmental factors (surface area, depth, alkalinity, chlorophyll-a, total phosphorus) influenced fish body condition. Permutation tests and adjusted R² confirmed that diet composition varied by size in walleye but not for perch or pike, while environmental factors had species-specific effects on body condition. Associated scripts and code required to replicate all analyses in the manuscript are provided.