Common Carp Are Initially Repelled by a Broadband Outboard Motor Sound in a Lock Chamber but Habituate Rapidly

Projecting sound into navigational locks has been suggested as a promising way to block the upstream movement of invasive species of carp (family Cyprinidae). This possibility is promising because carp have a good sense of hearing compared to non‐ostariophysian fishes. Although the broadband sound of an outboard motor has been shown to repel several species of carp in laboratory arenas, its efficacy in a navigational lock is unknown. This study tested whether wild‐caught Common Carp Cyprinus carpio are repelled by this sound in a lock chamber in a similar manner to that observed in laboratory studies. We found that while the sound of a 40‐hp outboard motor repelled Common Carp in a lock the first time it was tested, the fish stopped responding after that, suggesting that they had habituated. This result differed from that of a laboratory study that used the same sound at the same volume and found responses to persist for three exposures before dissipating. Many factors, including the use of wild Common Carp already familiar with outboard motor sounds and differences in background noise, may have been responsible for differences between laboratory and field results. There is a need for more field tests using other sounds and carp species.