To study the behavior of dolphinfish (Coryphaena hippurus) around drifting Fish Aggregating Devices (FADs), we tagged individuals with long-lived, coded sonic
transmitters and attached automated sonic receivers to drifting FADs in two
regions of the Western Indian Ocean. Among the three tagging methods used in
this study (surgery, external hooks, underwater bait without capture), the
latest resulted in residence times significantly shorter than the other
ones, likely due to regurgitation. Dolphinfish tagged with the two other
methods usually stayed several days associated to FADs (Kaplan-Meier
survival analysis 5.09 days, mean 6.25 days, SD 4.39 days, maximum 15.26
days), drifting with them. There was no significant difference in the
residence times of dolphinfish in equatorial and tropical areas. While
associated to FADs, dolphinfish spent most of their time close to floating
object (<365 m). The total time spent away from FADs was low (median
8%), and likely corresponded to making feeding excursions. Dolphinfish
did not form a single school while associated to a given FADs, but formed
multiple small schools. FADs are likely to be sites with exchanges of
individuals between schools. These results are discussed in regards to the
possibility of FADs acting as ecological traps and the validity of
meeting-point hypotheses as an explanation for fish aggregations under
floating objects.