Manual Acoustic Tracking Reveals the Spatial Ecology of Giant Trevally at a Remote South Pacific Atoll, with Implications for Their Management

Giant trevally (Caranx ignobilis) are important predators on the reefs of the tropical Indo-Pacific and research into their spatial ecology is needed to improve our understanding of their behavior and assist fisheries management. We used active acoustic telemetry to describe the fine-scale movements of giant trevally at Tetiaroa Atoll, including their home range, site fidelity, habitat use and spatial overlap with a small (21 km2) Marine Protected Area (MPA). The home ranges of giant trevally were small but varied among individuals (Minimum Convex Polygon 𝑋𝑋 = 3.2 ± 2.5 km2). All giant trevally exhibited site fidelity to their respective home ranges with a 31% average overlap in daily space use, but there was limited overlap in home ranges among individuals, with intra-individual spatial overlap significantly greater than inter-individual overlap (t = -4.93, df = 16.87, p-value = <0.001). There was only modest overlap (19 ± 19%) of giant trevally home ranges within the MPA and high spatial overlap of home ranges with deep lagoon habitats (90 ± 0.09 %). Our results indicate that MPAs could be an effective tool for the conservation of this species if they are implemented on an atoll-wide scale. However, in the case of managing recreational catch-and-release fisheries, rotational smallscale temporal closures could be effective in regulating the angling pressure imposed upon giant trevally, provided post-release mortality is minimized. The results of this study provide the first detailed account of habitat use in this species and highlight the need for additional research on the factors contributing to the survival of caught-and-released giant trevally in predator dominated atolls, especially as their popularity as a target of recreational fisheries continues to grow, and fishing operations and agencies are faced with the need to manage their fisheries.