Open-Water Orientation of White Bass, Roccus chrysops, as Determined by Ultrasonic Tracking Methods

Abstract

In the spring and summer of 1965, 26 white bass, Roccus chrysops (Rafinesque), were displaced to open water on Lake Mendota, Wisconsin, and their paths traced by means of ultrasonic transmitters carried in the stomachs of the fish and receiving gear located on boats. Seventeen fish captured by fyke nets on their spawning ground were displaced 1.6 km west-southwest to a mid lake release point. Two months after the spawning season nine fish, captured by hook-and-line, were displaced 3.1 km east-northeast from their capture area to the same release point. The mean tracking time for all 26 fish was 7.31 hr.Both the spawning and nonspawning fish maintained steady courses over long distances, and both groups showed a distinct directional preference for the eastern half of the lake where the spawning grounds are located. This open-water orientation helps explain the rapid homing performance, observed in previous experiments, of displaced spawning white bass, and also demonstrates that white bass possess mechanisms for orienting to directional cues present in their natural environment.Water currents, wind-generated surface waves, and the sun were examined as possible directional cues used by the fish. Although there was some evidence supporting the use of each of these cues, the problem of orientation mechanisms remains obscure. It was determined, however, that the observed movements of the fish cannot be explained as simply passive drift by the water currents.