Movements of Rainbow Steelhead Trout (Salmo Gairdneri) in Lake Ontario and a Hypothesis for the Influence of Spring Thermal Structure

Abstract

To examine movements of rainbow/steelhead trout (Salmo gairdneri) and associated environmental influences, 28 fish were radiotagged in and near a tributary of Lake Ontario during spring spawning runs in 1981 and 1982. Trout initially entering the lake from the tributary generally exhibited east-west reversals of movement along the southern shore of Lake Ontario before dispersing offshore. Seasonal movement rates averages 3.2 +/- 1.6 km/d over periods of 6 - 94 d; mean short term rates were 0.50 +/- 0.46 km/h. Temperatures occupied in the lake were 9.1 +/- 3.8 degrees C. Movements offshore and ultimate disappearances occurred from April to July, but were most pronounced when temperatures near shore exceeded 10 degrees C. By linking trout movements to seasonal thermal structure in Lake Ontario, a testable hypothesis was established to explain the distribution of rainbow trout in spring and early summer. Based on tracking data, information provided by south shore anglers, and literature on the physical limnology of Lake Ontario, we hypothesize that rainbow trout disperse off shore in spring with thermal fronts, particularly in the 6 - 8 degree C zone known as the spring thermocline.