Temporal dynamics, residency and site fidelity of spawning aggregations of a herbivorous tropical reef fish Siganus sutor

The shoemaker spinefoot Siganus sutor is a fast-growing, short-lived, gonochorist and herbivorous reef fish that forms transient fish spawning aggregations (FSAs). In the Seychelles, FSAs of this species occur monthly between September and June around the full moon. To study the spawning aggregation dynamics of S. sutor, 39 reproductively active individuals were acoustically tagged and monitored at 3 known FSA sites (Paté Polite, Paté Désiré and Paté Dividi) off the west coast of Praslin island (Seychelles) between October 2010 and April 2011. The presence and absence of tagged fish at the 3 sites were monitored using moored arrays of passive acoustic receivers, while the density of fish at the FSAs was quantified using underwater visual census (UVC). Most tagged fish (87.0%) detected in more than 1 spawning period showed fidelity to single spawning sites. Predominantly, tagged individuals arrived at FSA sites at dawn and departed at dusk. Spawning residency times at FSA sites ranged from 0.02 to 16.1 d. At Paté Polite, residency times were higher in the first half of the spawning season. Residency times were often several-fold shorter than aggregation duration which, when combined with patterns in arrival and departure times, indicates high turnover of fish within aggregations. The findings of this study provide information needed for emerging co-management schemes that aim to sustain this socio-economically important fishery.