Size-Dependent Winter Mortality of Young-of-the-Year White Perch: Climate Warming and Invasion of the Laurentian Great Lakes

White perch Morone americana invaded Lake Ontario about 1946 and are now found in Lakes Erie, St. Clair, and Huron, and in Green Bay, Lake Michigan. The indigenous marine distribution of white perch along the Atlantic coast of North America and analysis of climatological data suggest that the northern Gulf of St. Lawrence in the vicinity of the Gasp& Peninsula is too cold to permit white perch to establish local populations or to invade the Great Lakes via the St. Lawrence River. High mortalities of white perch have occurred in Lake Ontario during very cold winters, further suggesting that distribution of white perch is limited by low tolerance of cold temperature. Warmer-than-average summer and winter temperatures during the late 1940s coincided with the invasion of white perch into the Great Lakes via transportation canals in the state of New York. Tolerance of young-of-the-year white perch for low temperature was tested in the laboratory in overwinter experiments at constant temperatures of 2.5° and 4.0°C. Winter mortality was strongly influenced by body size, winter duration, temperature, and food availability. At 4.0°C, mortality was high for the smallest fish when food was withheld, but no mortality occurred under ad libitum feeding. The observed mortality for starved fish held at 4.0°C for 180 d was 40.6%. Expressed as a function of winter duration (WD, the number of daysˈ exposure to 4.0 or 2.5°C) and fork length (FL), the probability of mortality (PMORT) was: PMORT = 7.29543·e0.02145WD–0.10804FL. At 2.5°C, observed mortality was much higher than at 4°C (68.4% after 150 d) and body size and winter duration continued to have strong effects: PMORT = 0.28054·e0.01862WD–0.03097FL. Our results suggest that continued climate warming due to the “greenhouse effect” would lead to improved recruitment and expansion of the range of white perch in the Great Lakes, because growth and size of young-of-the-year fish would be enhanced by longer growing seasons and winters would be shorter and less severe.