Ultrasonic Tracking of Homing Cutthroat Trout (Salmo clarki) in Yellowstone Lake

Abstract

Displacement of 42 mature cutthroat trout (Salmo clarki) from their spawning tributaries to the open water of Yellowstone Lake in the summers of 1966 and 1968 and following them ultrasonically up to 13.5 hr and 11.8 km indicated that those that homed used a compass mechanism rather than search or true navigation to find shore and then followed the shoreline to the home stream. Vision was unnecessary for homing. For many of the fish whose movements showed no consistent pattern, the transmitters failed prematurely.Of 29 nonanesthetized trout tracked from a point northwest of their home streams, six moved generally eastward to shallow water, turned south, and followed the shoreline toward the home streams, three being followed all the way home. Six moved generally south or southeast and progressed toward their home streams entirely in open water, one being followed home. Three moved inappropriately for homing but were less than 2 km from the release point when tracking was ended. Fourteen moved randomly or did not move enough or were not tracked long enough to establish a pattern.Of five anesthetized-blinded trout, two moved eastward and then south along the shoreline, one moved south in open water, and the other two did not show a consistent pattern. Of four anesthetized-control trout, two moved eastward and then south along shore, one being followed home; one moved inappropriately and the other did not establish a pattern.Of four nonanesthetized trout tracked from a point southwest of their home stream, three moved east and then north along shore toward the home stream, one being followed home; the fourth moved north in open water.Current directions may have influenced the initial orientations.Swimming speeds ranged from 0.0 to 46.2 cm sec−1 in open water and from 8.5 to 82.3 cm sec−1 along shore. Average along-shore speed (36.6 cm sec−1) was greater than average open-water speed (22.9 cm sec−1). Blinded trout swam at about the same speeds (average 22.6 cm sec−1) as control trout (average 27.0 cm sec−1) and nonanesthetized trout (average 23.3 cm sec−1).