| Sculpin (Cottus pollux) is a weak swimmer. Our experimental study shows that only a 15-cm drop prevents their migration, even though their maximum swimming speed is not particularly slow. We propose a method to improve their migration based on two patterns of swimming behavior observed around artificial structures. One swimming pattern is to almost slide or creep along the bottom, splaying their pectoral fin. The other is moving in a kind of arc, before squaring their ventral fin. It is assumed that water depth and flow velocity are related to these swimming patterns. The latter pattern prevents their migration on high velocity flow, because they cannot control their migration due to upper pressure on the belly. From these results, it is considered necessary to reduce the flow velocities near the bottom for sculpin migration. Also, a high-density refuge will help avoid their failure to migrate. The combination of various roughnesses effectively improves their migration. |
