Life-stage–specific habitat associations and detection patterns of pākuʻikuʻi (Acanthurus achilles) on Hawaiʻi Island reefs

Abstract

Monitoring coral reef fishes is essential for assessing ecosystem health and managing fisheries, yet it remains challenging due to imperfect detection, complex habitats, shifting environmental conditions, and life-stage-specific behaviors. Detection–occupancy models address these limitations by separating detection probability from true occupancy. This study applied a single-season, multi-method (diver vs. remotely operated vehicle, ROV) single- and two-species (juvenile vs. adult) detection–occupancy framework to pākuʻikuʻi (Achilles Tang, Acanthurus achilles), a culturally, ecologically, and economically important reef fish in both commercial and noncommercial fisheries experiencing population decline along the west coast of Hawaiʻi Island. Fifty-two sites around Hawai‘i Island were surveyed 3–4 times using combinations of SCUBA, snorkel, and ROV methods, and models incorporated environmental covariates representing human, oceanographic, and habitat conditions. Juveniles showed stronger associations with habitat conditions, including coral cover and relative slope, whereas adult occupancy was linked to broader oceanographic and human-based gradients. Adults were more likely to occur at sites where juveniles were present, suggesting habitat connectivity across life stages. Detection probabilities were comparable between survey methods, indicating that integrating ROV surveys may enhance monitoring efficiency and spatial coverage. Collectively, these findings demonstrate that accounting for imperfect detection improves inference about population status and habitat relationships for species with cryptic or ontogenetically shifting behavior. By modeling key habitat drivers and highlighting co-occurrence between life stages, this study provides actionable insight and a scalable framework to support recovery planning and adaptive management for an imperiled species on Hawaiʻi’s nearshore reefs.