Incorporation of carbon and nitrogen isotopes in age-0 walleye (Sander vitreus) tissues following a laboratory diet switch experiment

Abstract

Trophic dynamics are often described by following the exchange of naturally occurring isotopes through aquatic communities. However, without experimentally derived isotopic turnover rates and discrimination factors for each species, tissue, and life stage, these trophic models can be misleading. We conducted a laboratory diet shift experiment to describe isotopic turnover and discrimination in age-0 walleye (Sander vitreus) dorsal muscle and gutted carcass samples. Although turnover of dietary δ13C (half-life: 10–12 days) and δ15N (half-life: ∼13 days) signatures was relatively rapid, the diet change was undetected in both tissues during a short transitional period (up to 1.2 times shorter in muscle). Our discrimination estimates generally conform to those of other fishes (ΔCarbon= 0.91, ΔNitrogen= 1.6), but were 30%–50% higher in muscle tissues than in gutted carcass samples. The assumption that young walleye tissues are in equilibrium with their diet is untrue for weeks following a diet shift, and when incorporated, discrimination factors differ between tissues. We provide tissue-specific parameters that remove uncertainty associated with the analysis of field collected isotopic age-0 walleye data.