Impending extirpation of an isolated Nassau grouper (Epinephelus striatus) population at Glover’s Atoll, Belize, based on two decades of monitoring

Abstract Nassau grouper (Epinephelus striatus) was once among the most abundant and commercially important reef fish species in the Caribbean region. Overextraction at their fish spawning aggregations (FSAs) has contributed significantly to dramatic regionwide declines in their populations, resulting in widespread local extirpations, nominal presence in catch composition and categorization as an IUCN critically endangered species. This study reviews over 20 years of fishery-dependent and fishery-independent observations to examine the status of a spatially isolated population of Nassau Grouper inhabiting Glover’s Atoll, Belize (which is wholly encompassed by Glover’s Reef Marine Reserve) and utilizing a single well-documented reproductive site. Nassau grouper at Glover’s Reef Marine Reserve has decreased in abundance by 85% at the spawning site and decreased in density to virtually undetectable levels across all habitats and management zones despite seasonal and spatial closures, upper and lower size limits and collaborative monitoring and enforcement since 2003. Nassau grouper is also extremely rare in fisher catches both at Glover’s Reef Marine Reserve (n = 118 over 20 years) and nationally (18 of 18,383 fish observed at landing sites between 2017 and 2020), with juvenile fish comprising over 75% of the sampled individuals. The population at Glover’s Reef Marine Reserve continues to decline on a trajectory towards local extirpation. Closure of management gaps, including chronic enforcement resource deficits, may not guarantee recovery but has been a necessary precursor to recovery of other FSAs in the Caribbean.