Local resource reliance of juvenile fish in small lakes

Abstract

AbstractJuvenile stages of fishes are frequently bottlenecks to recruitment. Habitat use of early life stages and the extent to which fish rely on local resources may affect how they respond to habitat loss and alterations, with important implications for habitat management. To investigate the potential for prolonged reliance on local resources, we quantified stable isotope ratios (δ13 carbon, δ15 nitrogen, δ18 oxygen and δ2 hydrogen) of young‐of‐year (YOY) largemouth bass Micropterus salmoides and isotope ratios of locally collected water and potential prey across three study components, a controlled pond experiment, a multi‐lake survey and a detailed single‐lake survey. Across study components, we observed habitat and site fidelity of YOY largemouth bass in mid‐summer, demonstrated by distinct spatial differences in young bass stable isotope ratios. Additionally, we observed significant, positive correlations between δ13C of YOY largemouth bass and δ13C of locally collected invertebrates and small bluegill Lepomis macrochirus in the single lake survey, suggesting localised foraging. Later in summer, spatial differences in largemouth bass stable isotope ratios were not apparent, indicating a transition to more spatially integrated foraging. Prior to switch to piscivory, YOY largemouth bass rely on local resources indicating that they may be more susceptible, both positively and negatively, to hyper‐local changes in forage availability or disturbances. This study demonstrates that stable isotope ratios allow for differentiating environmental experiences among young fish in relatively close proximity in small freshwater systems. Moreover, high spatial variation of consumer stable isotope ratios demonstrates the importance of considering spatial heterogeneity in stable isotope studies.