These large fish are associated with hard structure such as reefs (both natural and artificial), rocks, and ledges. It was easy for commercial and recreational fisherman to catch Nassau grouper and it soon became scarce.
Because their range exceeds national borders, the best approach to their conservation is regional closed seasons. Sampling of fish landed in the U.S. Virgin Islands and Puerto Rico during the 1970s and 1980s indicates that Nassau grouper were commonly caught, mostly from spawning aggregation sites.
Currently, Nassau grouper are occasionally reported during underwater reef surveys at low density. Coloration varies, but adult fish are generally light beige, with five dark brown vertical bars, a large black saddle blotch on top of the base of the tail, and a row of black spots below and behind each eye.
A dark band that forms a tuning-fork pattern on top of the head, beginning at the front of the upper jaw, extending through each eye, and then curving to meet its corresponding band in front of the dorsal fin. They can be distinguished from other groupers by the vertical bars and dark saddle coloring along the dorsal part of the area preceding the tail.
Color pattern can change within minutes from almost white too bicolored to uniformly dark brown, according to the behavioral state of the fish. They take advantage of lower light levels at dawn and dusk, combined with the higher number of prey during changeover between diurnal and nocturnal fishes.
Nassau grouper are found in tropical and subtropical waters of the western North Atlantic. This includes Bermuda, Florida, Bahamas, the Yucatán Peninsula, and throughout the Caribbean to southern Brazil.
There has been one verified report of Nassau grouper in the Gulf of Mexico at Flower Gardens Bank. The Nassau grouper is considered a reef fish, but it transitions as it grows through a series of shifts in both habitat and diet.
As juveniles, they are found in nearshore shallow waters in macro algal and seagrass habitats. The main influences on where they live are not known, though water clarity, habitat, and bent hos (the community of organisms in the seabed) seem to be important.
Nassau grouper tend to spend a lot of time in one spot, often on a high-relief coral reefs or rocks in clear water. Larger fish tend to occupy deeper reef areas with greater vertical relief.
While adult Nassau groupers can change sex after hormone injection, natural sex-change has not been confirmed. Sites have been found near the edges of reefs, as little as 50 yards from the shore, near drop-offs into deeper water across a wide range of depths (20 to 200 feet) and environments (including soft corals, sponges, stony coral outcrops, and sandy depressions).
Some more information on how Nassau grouper get to their spawning sites, based on limited observations: After 1 to 2 months of floating with the ocean currents, the larvae settle in nearshore shallow waters in macro algal and seagrass habitats.
Adults are relatively solitary, living in areas that (patchily) overlap other groupers’ home ranges. In some countries with protective regulations, there are too few enforcement officers to cover a large geographic area with many landing locations.
Superimposed on this base color are a number of lighter stripes, darker spots, bars, and patterns, including black spots below and behind the eye, and a forked stripe on the top of the head. By the light of the full moon, huge numbers of the grouper cluster together to mate in mass spawning.
The Nassau grouper is fished both commercially and for sport; it is less shy than other groupers, and is readily approached by scuba divers. However, its numbers have been sharply reduced by overfishing in recent years, and it is a slow breeder.
Furthermore, its historic spawning areas are easily targeted for fishing, which tends to remove the reproductively active members of the group. The species is therefore highly vulnerable to overexploitation, and is recognized as critically endangered on the IUCN Red List.
The governments of the United States, the Cayman Islands, and the Bahamas have banned or instituted closed fishing seasons for the Nassau grouper in recent years. In the Cayman Islands, fishing in the spawning holes of the grouper has been banned until the end of 2016.
A large spawning site for the species is located at Glover's Reef, off the Belizean coast. It has been identified as one of only two viable sites remaining for the species, of 9 originally known locations.
However, the Nassaugrouper's spawning region is not included in this marine protected area (MPA). Many conservation methods have been put in place to help the grouper, including closed seasons, when fishing is not allowed.
Some areas are protected, a complete ban on fishing the grouper in US waters has been instituted. However, analysis of declines in both populations and the size spawning aggregations has led to the species being uplifted to critically endangered by the IUCN Red List in 2018.
The Nassau grouper has been depicted on postage stamps of Cuba (1965, 1975), the Bahamas (1971 5-cent), and Antigua and Barbuda (1987 40-c). The Nassau grouper was placed on the World Conservation Union's realist of threatened species in 1996, and it was determined to be endangered because its population has declined by 60% in the past 30 years.
Over a third of spawning aggregations have been estimated to have disappeared, and the grouper is considered to be commercially extinct in some areas. The current population is estimated to be more than 10,000 mature individuals, but is thought to be decreasing.
^ Shcherbina, Andrey; Glen G. Gawarkiewicz; Christopher A. Liner; Simon R. Horror (Sep 2008). “Mapping bathymetric and hydrographic features of Glover's Reef, Belize, with a REMUS autonomous underwater vehicle” (PDF).