SOUND PRODUCTION THROUGH THE SUBSTRATE DURING REPRODUCTION IN THE MOTTLED SCULPIN, COTTUS-BAIRDI (COTTIDAE)

During reproduction male Cottus bairdi defend cavities beneath stones and perform defense and reproductive displays. Using a geophone to det ect substrate vibrations under dark conditions (infrared viewing), we recorded three types of sounds. 'Knocks' are produced during head nods and an acoustically similar sound is produced when the fish slaps the head to the substrate. A third sound, the 'drum roll' appears to be a fast repetition of several knocks followed by a head slap. We argue t hat these signals traveling through the substrate are of greater impor tance than sounds traveling through the water because (1) the substrat e vibration attenuates at a much lesser rate than the water vibration and, (2) even near riffles, which generate much water vibration, the b ackground noise in the substrate is low enough for the fish to detect such sounds.