Movement Patterns and Habitat use of Adult Giant Trevally (Caranx Ignobilis) in the South China Sea

Abstract This paper presents the first application of pop-up satellite archival tags (PSATs) to giant trevally (Caranx ignobilis) in a "no-take" marine protected area (MPA) comprising in a major reef system in the South China Sea (Dongsha Attol National Park). In order to determine appropriate management strategies in an around the MPA and to delimit stock boundaries to help restore populations, fundamental ecological information is required on movement patterns, habitat preferences and home range. In total 10 giant trevally were tagged from May 2016 to September 2018. Eight tags reported and remained affixed from 17 to 243 days and linear displacements ranged from 26 to 826 km from deployment to pop-up locations. Fish were mainly confined to the mixed-layer but occasionally made deeper descents (~50 -60 m) during nighttime and the distributions of time spent at depth (~0 - 67 m) and temperature (21.5 - 35.4°C) were significantly different between daytime and nighttime but the transitions were not pronounced. Most probable tracks calculated from a state-space Kalman filter suggested site-fidelity and/or cyclic N-S dispersal patterns possibly related to spawning or foraging as about half of the pop-up locations were within ~100 km of the tagging location. Given these findings and implications, it is possible that giant trevally may need to be managed at small spatial scales to preserve genetic diversity. Additional tagging studies, however, using genetic data and conventional tags to maximize cost-benefit and augmented with a sub-set of PSATs, will be required to test this hypothesis at a higher level of statistical power.