Nassau grouper migration patterns during full moon suggest collapsed historic fish spawning aggregation and evidence of an undocumented aggregation

Many fish species migrate to form fish spawning aggregations. The temporal and spatial predictability of these migrations and spawning aggregation locations makes species vulnerable to overfishing, as the majority of an adult population within a large region may be harvested quickly with minimal effort. Historically, the Nassau grouper, Epinephelus striatus (Bloch, 1792), was an important fishery species throughout its range, but due to spawning aggregation overfishing, it is now rare in many reef ecosystems. In The Bahamas, stocks continue to decline despite the implementation of spawning aggregation protections. While more Nassau grouper spawning aggregations have been reported in The Bahamas than any other country, very few have been validated, and the dynamics of spawning migrations to and from these sites is poorly understood. Here, we used acoustic telemetry to describe, for the first time, Nassau grouper migrations along Andros Island, The Bahamas, which is bordered by one of the longest barrier reefs in the world. We report the likely extirpation of a historically important spawning aggregation and suggest Nassau grouper are migrating to a previously undocumented spawning location. Fish migrated in groups during the January 2015 full moon along the barrier reef shelf edge traveling roundtrip distances of 71.5–260.3 km [x = 164.5 (SD 65.7) km, n = 9]. These results are critical to assess the efficacy of current management strategies in The Bahamas. Thus far, all known spaning aggregations have been reported to the scientific community by fishers. Data from our study, however, suggest the presence of a potential spawning aggregation informed by passive telemetry and warrants further investigation.