Analyzing the shift to piscivory in age-0 largemouth bass using stable isotopes
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Date
2017-05
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The Ohio State University
Abstract
Many animals undergo diet shifts during early life as ability to capture larger prey increases with growth. For largemouth bass (Micropterus salmoides), this is characterized by a diet transition from zooplankton to fish. In this study, we aimed to quantify the timing of this shift to piscivory in juvenile largemouth bass from two Ohio reservoirs, Deer Creek and Burr Oak lakes. We hypothesized that the faster growth rates observed in Deer Creek Lake were due to earlier shifts to piscivory. We measured carbon (δ13C) and nitrogen (δ15N) isotope ratios in juvenile largemouth bass and their potential prey species, including zooplankton, macroinvertebrates, and larval fish, as an indirect assessment of past diets in juvenile bass. Samples were collected June-August 2014. Trophic position was calculated by comparing the δ15N of largemouth bass to the baseline δ15N of larval fish. We found an increase in trophic position over the observation period in juvenile largemouth bass from Deer Creek Lake (p < 0.001), suggesting a switch to piscivory, but not in Burr Oak Lake (p = 0.36). In both reservoirs, trophic position was positively correlated to juvenile bass length. δ15N of zooplankton, macroinvertebrates, and larval fish varied significantly through the season in Deer Creek Lake (p = 0.02) and Burr Oak Lake (p = 0.03). δ13C of baseline prey items from both reservoirs increased through the season. We hypothesize that these trends were due to watershed inputs, nitrogen-fixing bacteria, and spatial variation. We conclude that 1) juvenile largemouth bass became at least partially piscivorous in Deer Creek Lake during the study period and 2) stable isotopes as a tool to identify prey sources may have limited effectiveness in these reservoirs because of variability in isotopic signatures of the incoming water.
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2nd place in the Denman Forum
Keywords
isotopes, piscivory, diet, bass, juvenile