Challenge of monitoring cohesive movement in homing fish using fine-scale 3d positioning

Abstract

Rockfish, which are well known for their site fidelity and homing ability, live sym-patrically with many conspecifics. Conspecifics may be external drivers influencing rockfish movement, and rockfish may move cohesively while travelling. We tested whether rockfish formed a group when returning to their original habitat after artificial displacement and examined the routes they travelled to return home. A fine-scale multi-individual simultaneous positioning method was used to observe the movement trajectories of tagged fish. Our results showed that tagged fish, released in groups, returned to their original habitat (5 of 8 fish) but generally did not travel with other individuals. There was one exception in which 2 individuals moved together for ~100 s immediately after release. These 2 fish had no designated leader, alternating as leader and follower. Our hypothesis was partially corroborated by these rockfish possibly travelling cohe-sively. The returning fish tended to travel along the sea bottom and the coastline, independent of current; thus, they likely used visual cues, rather than olfactory or social cues, to return home.