Underwater Noise Spectra, Fish Sounds and Response to Low Frequencies of Cutthroat Trout with Reference to Orientation and Homing in Yellowstone Lake

Underwater ambient noise was investigated in the stream-mouths of Clear, Cub and Pelican Creeks. Noise levels were determined from 0.1 to 10 KHz during periods of high stream discharge and wave action. Minimum noise levels could not be determined due to instrument noise interference. Two noise sources contributed to ambient pressure spectrum levels in the stream-mouths: (1) flow noise and/or bubbles, and (2) surf-beats. The former is mainly composed of frequencies below 4 KHz while the latter is above 5 KHz. Four cutthroat trout (Salmo clarki) sounds were recorded and analyzed. The \u27thump\u27 sound occurred when fish were alarmed and gave a sudden tail-flip. The principal frequency was 150 Hz in the band from 100 to 200 Hz. The \u27squawk\u27 sound had principal frequencies in the band from 600 to 850 Hz. The \u27squeak\u27 sound was infrequent and usually of low intensity. A sound with maximum energy above 2 KHz was created when a trout shifted bottom materials while preparing a redd. The response to low frequency sound was tested with 29 cutthroat trout. The conditioned response technique was applied using shock or light as the unconditioned stimulus. A positive response was not readily obtained. A natural response to sound stimuli was found in six fish with an average upper frequency limit of 443 Hz. Underwater sounds are within the range of fish perception but it was not determined if homing fish recognized or utilized stream noises