Distribution, Persistence, and Growth of Groupers (Pisces: Serranidae) on Artificial and Natural Patch Reefs in the Virgin Islands

We examined patterns of distribution, persistence, and growth of groupers (especially Nassau grouper, Epinephelus striatus), which recruited to or colonized 52 one cubic-meter concrete-block reefs and 10 natural patch reefs off St. Thomas, USVI. The artificial reefs comprised five shelter treatments: 24 large holes, 12 large holes, 24 small holes, 12 small holes, and holeless controls. Although small individuals (<15 cm TL) of the two most abundant species, E. striatus and E. afer, were distributed evenly among these treatments, larger individuals were usually more abundant on large-hole reefs, E. striatus and E. afer partitioned the artificial reefs by depth, ranging from 6 to 12 m, with E. striatus occurring deeper than E. afer. Tagged individuals demonstrated persistence on and homing to specific reefs. Overall, Nassau grouper was the most abundant of six species of Epinephelus observed on the artificial reefs. However, this was not the case on natural reefs or in commercial catches, which were dominated by E. cruentatus, E. fulvus, and E. guttatus. Growth rates of a distinct recruit cohort of Nassau grouper on the artificial reefs were comparable to those estimated in other recent field studies. Mean monthly growth rates ranged from 0.84 to 1.17 cm·month⁻¹, and mean growth from the first month of observation (mean size = 8.7 cm) through the eleventh month (19.5 cm) was 10.8 cm. Persistence of the cohort during the year was low, with an 85.4% decline from 158 to 23 individuals over 8 months, presumably due to predation. Due to apparent recruitment overfishing caused by decimation of the local spawning aggregation off St. Thomas, Nassau grouper catches have declined dramatically in recent years. Given the differential distribution of adult Nassau grouper between artificial and natural reefs, we conclude that artificial reefs of the appropriate design may enhance the local abundance of this commercially valuable species.