Modeling the preference of ayu (Plecoglossus altivelis) for underwater sounds to determine the migration path in a river

Water sounds are believed to be important in triggering the upriver ascent behavior of migratory fish species. Modeling the effect of underwater sound on fish preference represents a promising technique to determine migratory paths for the comprehensive analysis of river habitat suitability. In this study, we aimed to determine the preference and weight of underwater sounds by laboratory experiments using adult and juvenile ayu (Plecoglossus altivelis). A watercourse with an underwater speaker installed at one end was used for the experiments. Sound was emitted from the speaker at different sound pressure levels. The sound sources included pure tones (100 Hz, 200 Hz, 400 Hz, and 800 Hz), white noise, recorded sound from a weir on the Fushino River, and recorded sound at a fish ladder on the Misumi River (Japan). The results showed that juvenile and adult ayu avoided the pure sound of 100 Hz and recorded sound of the Fushino River weir. In contrast, both adults and juveniles preferred the pure sound of 200 Hz and recorded sound of the fish ladder. Moreover, by comparing the obtained quantitative preference parameters for sounds, we found that adult ayu expressed higher preference for sound than juveniles. We designed a procedure to calculate sound preference and built it into our fish behavior simulation model on geographic information system (GIS) software. We believe that the model could successfully reproduce observed fish migration behavior in rivers. This technique could be used for designing an underwater soundscape to attract fish to the entrances of fish ladders or to keep fish away from hydropower plants.