Estimation of spawning migration distance of the white-streaked grouper (Epinephelus ongus) in an Okinawan coral reef system using conventional tag-and-release

Abstract

The white-streaked grouper (Epinephelus ongus) is an important fisheries target in the region around Okinawa. This species forms spawning aggre- gations at specific spawning grounds in the last-quarter of the moon in April and/or May. Using a tag-and- release method, we estimated the migration distance and the degree of unified movement of groupers asso- ciated with the spawning migration. In total, 1157 E. ongus individuals were tagged and released at their homegrounds inthenon-spawningperiodand350 were tagged at a known spawning ground (Yonara Channel) in the spawningperiod. For the fish that were releasedat the home grounds, 23 individuals were recaptured at the spawning ground during in the spawning periods. For the individuals that were released at the spawning ground, six individuals were recaptured outside of the spawning ground. The estimated migration distances from the home ground to the spawning ground ranged from 2.2 to 8.8 km. There was no significant relation- ship between the fish total length (TL) and migration distance for both males and females. Tagged individuals inhabiting the same home ground were recaptured at different points at the spawning ground separated by a distance of over several hundred meters. Furthermore, tagged individuals that were released at the same point at the spawning ground were recaptured at different home grounds separated by a distance up to several kilometers. These results suggest that unified move- ments associated with the spawning migration are not high for E. ongus, which is contradict with some previ- ous studies suggesting the coordinated spawning migra- tion of other Epinephelus spp.