Movement patterns and space usage of giant trevally, Caranx ignobilis, in Hawaiian waters

Abstract

Giant trevally ("ulua", Caranx ignobilis) are large, mobile mesopredators found around coral reefs ecosystems across the Indo-Pacific. Despite their cultural significance, popularity in recreational fisheries, and likely importance in coral reef ecosystems, we lack key basic knowledge about their spatial use and movement patterns. I used the largest acoustic telemetry dataset of ulua to date (166 tagged individuals collectively monitored for 14 years), supplemented by fine-scale movement data from active acoustic tracking of three individuals to quantify ulua site fidelity, space, and habitat requirements as well as ulua temporal patterns of movement across the Hawaiian Archipelago. Ulua showed moderate to high site fidelity to small home range areas typically 3.8 to 5.4 km in maximum linear dimension Overall, ulua had a depth range from the surface to a maximum depth of 242 m. There was evidence for more narrow depth ranges for individuals, but ulua depth distributions differed between regions. Ulua occasionally utilized a larger familiar area beyond their daily home range, with the size of this familiar area likely determined by the size of their ‘home’ island. There was no evidence of ulua moving across deep ocean channels between adjacent islands. Ulua movement patterns and habitat use were consistent with those of other coral reef fishes, albeit on a larger spatial scale. Though more information is needed for fine-scale movements across other Hawaiian islands, this thesis' conclusions on ulua spatial use and movement patterns will aid in data-driven management for the recreational and commercial fisheries, as well as provide broader understanding for a species that plays a key role in Hawaiian history and culture.