Effect of Broadband Boat Motor Sound on the Schooling Behavior of Invasive Bigheaded Carp

Introduction of silver (Hypophthalmichthys molitrix) and bighead (Hypophthalmichthys nobilis) carp to the Mississippi River drainage has created ecological and economic distress. These species, collectively known as bigheaded carp, are closely related, and silver carp are well known for their jumping behavior in response to motorboats. Therefore, the impact of boat motor sound on bigheaded carp behavior has important implications for controlling range expansion. We examined the effect of broadband boat motor sound on the schooling behavior of bigheaded carp. In a two-choice shuttle tank, broadband sound (0.06–10 kHz; 140 dB re: 1 μPa) was played via an underwater speaker, and bigheaded carp responses were recorded using overhead cameras. The schooling behavior of silver and bighead carp during broadband sound playback was compared to a no-sound period. Broadband sound playback elicited negative phonotaxis and increased swim speed in all trials. However, the carp continued to school (n = 5 individuals swimming in the same direction and one body length apart) the majority (57.2% ± 11.2%) of time during the broadband sound playback periods. These results indicate that schooling could contribute to the consistent negative phonotaxis observed in previous studies reporting the efficacy of broadband sound in deterring bigheaded carp swimming.