Seasonal Movements of the Winter Flounder, Pseudopleuronectes americanus (Walbaum), on the Atlantic Coast

Abstract

Winter flounders occur from Labrador to Georgia and yield large catches off southern New England. This paper relates their distribution and seasonal movements to environmental factors.In spring immature and mature flounders are alongshore with spawning fish concentrated in shallow water. During "summer", winter flounders leave the shore zone in areas where water temperatures rise above about 15 °C but not where bottom temperatures do not reach this level. This movement toward cooler water does not continue into depths at which temperature is below about 12 °C. Flounders return to the shore zone in fall after temperature decreases below 15 °C. These temperatures are well below the upper incipient lethal for flounders of about 26 °C.Flounders remaining alongshore in summer are distributed in depth according to size and maturity. Small, immature fish are in the shallowest water, the region of highest light intensity, immatures of medium size deeper, and mature fish in both regions. Under experimental conditions immature fish of medium size moved into shade at lower light intensities than either small immatures or large matures.North of Cape Cod flounders move deeper in "winter" as the shallow water becomes colder than the deeper. To the south spawning condition is reached earlier and mature flounders remain in shallow water during the cold-water period.Off southern New England a large, sustained fishery denotes a large population of flounders. In the Bay of Fundy and off the coast of Nova Scotia winter flounders are restricted to a narrow depth zone, and good exploratory catches there probably do not indicate large populations. In the broader shallow zones of the southern Gulf of St. Lawrence similar catches suggest a larger population. Exploitation will depend on increased efforts by small otter trawlers or possible development of marine sport fishing.