Role of current and daylight variations on small-pelagic fish aggregations around a coastal FAD from accurate acoustic tracking

TL;DR

This study investigates how current and daylight variations influence small pelagic fish aggregations around a coastal FAD, revealing displacement patterns and behavioral changes at dusk through acoustic tracking.

Contribution

It provides new insights into the behavioral responses of fish aggregations to environmental factors like current and light, using precise acoustic tracking around a floating device.

Findings

Current causes upstream displacement of fish aggregations.

Aggregation expands and becomes more coordinated at dusk.

Fish swim faster and align more at dusk.

Abstract

We monitored twelve acoustically-tagged small pelagic fish (Selar crumenophthalmus) around a floating object in shallow water, playing the role of a coastal fish aggregating device (FAD). We characterized the response of the tagged-fish aggregation to varying current strengths and daylight. We found that the current induced a displacement of the aggregation upstream of the FAD, at distances that were increasing with the current strength. We gave evidence, of an expansion and a higher coordination in the aggregation at dusk, with increasing swimming speed, distances among congeners and alignment. We discussed possible scenarios where fish polarization increases at dusk and proposed complementary measurements in future experiments that could confirm our findings.