The heterogeneous spatial and temporal patterns of behavior of small pelagic fish in an array of Fish Aggregating Devices (FADs)

摘要

Identifying spatial and temporal patterns can reveal the driving factors thatgovern the behavior of fish in their environment. In this study, wecharacterized the spatial and temporal occupation of 37 acoustically taggedbigeye scads (Selar Crumenophthalmus) in an array of shallow Fish AggregatingDevices (FADs) to clarify the mechanism that leads fish to associate with FADs.A comparison of the number of visits and residence times exhibited by the fishat different FADs revealed a strong variability over the array of FADS, withthe emergence of a leading FAD, which recorded the majority of visits andretained the fish for a longer period of time. We found diel variability in theresidence times, with fish associated at daytime and exploring the array ofFADs at nighttime. We demonstrated that this diel temporal pattern wasamplified in the leading FAD. We identified a 24-hour periodicity for a subsetof individuals aggregated to the leading FAD, thus suggesting that those fishwere able to find this FAD after night excursions. The modeling of fishmovements based on a Monte Carlo sampling of inter-FAD transitions revealedthat the observed spatial heterogeneity in the number of visits could not beexplained through simple array-connectivity arguments. Similarly, wedemonstrated that the high residence times recorded at the leading FAD were notdue to the spatial arrangement of individual fish having different associativecharacters. We discussed the relationships between these patterns ofassociation with the FADs, the exploration of the FAD array and the possibleeffects of social interactions and environmental factors.