Overwinter Growth and Survival of Largemouth Bass: Interactions among Size, Food, Origin, and Winter Severity

Abstract

Winter severity (temperature, duration, and photocycle), geographic origin, food availability, and initial body size likely influence growth, survival, and, therefore, recruitment of age-0 largemouth bass Micropterus salmoides. We collected age-0 largemouth bass (70–160 mm total length) from low (33°N), intermediate (40°N), and high (45°N) latitudes throughout their natural range (origin), and we subjected all three groups of fish to three experimental winters that mimicked these latitudes (N = 9 largemouth bass per treatment). Within each winter and origin, one-half of the largemouth bass were fed fish prey, whereas the remaining one-half were starved. Winter strongly influenced survival; overall survival rates in the high-, intermediate-, and low-latitude winters were 34.9, 59.4, and 61.1%, respectively (χ² test, P < 0.05). Largemouth bass from 33°N suffered high mortality in the high-latitude winter. Across all winters, more fed fish (64.5%) survived than did starved fish (38.1%) (χ² test, P < 0.05). Pooling fish into small (<100 mm) and large (≥100 mm) size classes revealed that more small fish died than did large fish in the low- and high-latitude winters, but this was not the case in the middle-latitude winter. Wet weights (g) of fed largemouth bass increased, remained constant, and declined in the low-, intermediate-, and high-latitude winters, respectively. Wet weights and total energy content (kJ) of fed individuals were consistently higher than those of their starved counterparts in all winters. However, energy density (kJ/g) of fed individuals often declined to levels similar to those of starved largemouth bass. Winter temperature combined with duration likely dictate the northern limit of largemouth bass by reducing growth, even when food is abundant. Because survival of individuals from the low latitude was poor in higher latitude winters, stocking southern largemouth bass in northern systems may translate to high mortality and perhaps to degradation of physiological tolerances of local populations through hybridization.