NASSAU GROUPER (ROCKFISH)
Nassau grouper (Scientific name: Epinephelus striatus) are also known as rockfish. They are largish medium-size fish associated typically found in reefs (both natural and artificial), rocks, and ledges. They are late-maturing, long-lived, top-level predators found in southern coastal Florida, the Florida Keys, Bermuda, the Yucatan, and the Caribbean Sea. Their lifespan in the wild is typically 12 to 16 years; there is a case of one caught estimated to be 29 years.[Sources: NOAA, Jordan Kime, Animal Diversity Web (ADW) /=]
Nassau grouper used to be one of the most common species of grouper in the United States. It was easy for commercial and recreational fisherman to catch Nassau grouper and it soon became scarce. The remaining stocks are overexploited. In some cases, Nassau grouper is commercially extinct through much of its geographical range. Currently, all harvest of Nassau grouper is prohibited in the United States. Because their range exceeds national borders, the best approach to their conservation is regional closed seasons.
Nassau grouper is listed as threatened throughout its range under the U.S. Endangered Species Act. Threats include bycatch, inadequate regulatory mechanisms and overfishing Based on the size and number of current spawning aggregations the Nassau grouper population appears to be just a fraction of its historical size. Data is scarce on historical Nassau grouper numbers. All groupers were reported together for fishery landings data, and specific data on Nassau grouper catch is limited. 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.
Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se ; Encyclopedia of Life eol.org ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Woods Hole Oceanographic Institute whoi.edu ; Cousteau Society cousteau.org ; Monterey Bay Aquarium montereybayaquarium.org ; MarineBio marinebio.org/oceans/creatures
Nassau Grouper Habitat and Where They Are Found
Nassau grouper are found in tropical and subtropical marine waters of the western North Atlantic. This includes Bermuda, Florida, Bahamas, the Yucatan Peninsula, and throughout the Caribbean to southern Brazil. They live in saltwater and marine environments as far north as the Carolinas. There has been one verified report of Nassau grouper in the Gulf of Mexico at Flower Gardens Bank.[Sources: NOAA, Jordan Kime, Animal Diversity Web (ADW) /=]
Nassau grouper are typically found at depths of one to 100 meters (3.28 to 328 feet) at an average depth of 30 meters (98 feet). Although they generally live among shallow reefs, they can be found in depths to 130 meters (426 feet).They can also be found in beds of sea grasses and prefer areas of high visibility. Late juveniles to young adults prefer corals with large macroalgal populations. This species is also euryhaline, meaning it can tolerate a wide range of salinities. During spawning, Nassau groupers can be found meters offshore, which has in part led to their exploitation and subsequent placement on the International Union for Conservation of Nature (IUCN) Red List.
The main influences on where they live are not known, though water clarity, habitat, and benthos (the community of organisms in the seabed) seem to be important. Their depth range may be influenced more by the availability of suitable habitat than by food resources, since their diet is highly varied and has more to do with body size than of water depth. 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. Both adults and juveniles will use either natural or artificial reefs.[Source: NOAA]
Nassau grouper are mostly absent from the continental United States — except Florida, where larger juveniles and adults have been recorded. No larval Nassau grouper or juveniles smaller than 20 inches in length have been collected or observed in Florida waters. However, sampling along shoreline habitats of the Florida Keys — where smaller juveniles might be expected — has been limited to date.[Source: NOAA]
Nassau Grouper Physical Characteristics
Nassau grouper are a moderate to large-sized fish that can grow up to 1.2 meters in length (almost four feet). They range in weight from two to 27 kilograms (4.41 to 59.47 pounds), with their average weight being 12 kilograms (26.43 pounds). They range in length from eight to 72 centimeters (3.15 to 28.35 inches), with their average length being 32 centimeters (12.60 inches). Sexual Dimorphism (differences between males and females) is apparent: Both sexes are roughly equal in size and look similar. One characteristic of Nassau groupers is a large black spot at the base of the tail. In juveniles, the caudal fin is rounded, whereas adults display a truncated fin characteristic of groupers. They can change coloration based on mood and behavior. [Sources: Jordan Kime, Animal Diversity Web (ADW) /=]
Nassau groupers have large eyes and a robust body and five dark, unevenly spaced bars across their body. A distinctive bar runs from the snout to the dorsal fin. Coloration varies from tawny to pinkish red, 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 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. [Source: NOAA]
Juveniles exhibit a color pattern similar to adults. 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 to bicolored to uniformly dark brown, according to the behavioral state of the fish. A distinctive bicolor pattern appears when two adults or an adult and large juvenile meet and is often seen at spawning aggregations.
Nassau Grouper Behavior
Nassau groupers are nocturnal (active at night), crepuscular (active at dawn and dusk), motile (move around as opposed to being stationary) and solitary. They are loyal to their home reef, returning there to spawn. Over the course of a year, a single Nassau grouper has been reported to move up to 220 kilometers. [Sources: Jordan Kime, Animal Diversity Web (ADW) /=]
Nassau groupers move in groups of 25 to 500. They travel parallel to the coast or along the shelf edge. Their movements are synchronous. When aggregating, Nassau grouper show three color “phases,” or patterns, along with their normal coloring. Their courtship takes place according to these phases. It ends near sunset, with a group of them swimming upward quickly; a female in the lead releases eggs, while the males behind her release sperm.[Source: NOAA]
Except while spawning, Nassau groupers are a solitary predators that prefer to stay close to reefs, wrecks or other protective cover. Adults live in areas that (patchily) overlap other groupers’ home ranges. The fish favor high-relief reef s and are typically inactive during the day and prefer to feed under the cover of darkness. According to Animal Diversity Web: Changes in color are often observed in relation to aggression during spawning, but occurs outside spawning. For example, when two Nassau groupers of different sizes meet, their body color may change in response to aggression. These color changes are not thought to be a camouflage or anti-predator adaptation. /=\
Nassau groupers communicate with vision and sense using vision, touch and chemicals usually detected with smell. They primarily communicate by altering their skin colors and patterns, especially when ready to spawn. Their normal barred color pattern is typically seen, but can become lighter, darker, or change to a bicoloration with a dark top and white bottom. This coloration may signify aggression and reception to spawning. /=\
Nassau Grouper Feeding and Predators
Nassau grouper are ambush predators that are not selective with their prey. They swallow prey whole using a suction created by their protruding mouth. Their mouth size determines the size of fish they eat. Adults eat mainly fish, while juveniles eat a variety of fish and invertebrates (such as, shrimp and crabs). As age and size increase, so do the preferred prey size. Smaller young adults prey on crustaceans and bivalves, while older Nassau groupers feed lobsters and gastropods in addition to fish. [Sources: NOAA, Jordan Kime, Animal Diversity Web (ADW) /=]
Nassau grouper feed predominantly at dawn and dusk, taking advantage of lower light levels at dawn and dusk, combined with the higher number of prey during changeover between diurnal and nocturnal fish. That timing would mean they need to use less energy in ambushing their prey. They have a unique method of engulfing its prey — quickly moving their gills to create suction, or negative pressure, that draws prey into their open mouth. Nassau groupers compete with other groupers because of overlapping habitat and also likely compete with snappers, jacks, barracudas, and sharks.
Given their size and habitat, Nassau groupers have few known predators other than humans, sharks and yellowtail snappers. Sharks occasionally attack groups of spawning Nassau groupers, and yellowtail snappers eat their eggs. Other predators may include moray eels, which prey on small groupers, and hammerhead and sandbar sharks, which prey on larger groupers. Nassau groupers practice cannibalism on occasion.
Nassau Grouper Mating and Reproduction
Nassau groupers are oviparous (young are hatched from eggs) and iteroparous (offspring are produced in groups). They are sequential hermaphrodites in which individuals change their sex at some point in their lives and typically produces eggs and sperm at different stages their lives, and are protogynous (hermaphrodites that have female organs and eggs before male organs and sperm). Nassau grouper pass through a juvenile bisexual phase, then mature directly as males or females. While adult Nassau groupers can change sex after hormone injection, natural sex-change has not been confirmed.[Sources: NOAA, Jordan Kime, Animal Diversity Web (ADW) /=]
Females and males reach sexual or reproductive maturity at two to seven years, on average at age five years. They typically mature when they reach about 15 to 17 inches. Most reach sexual maturity when they are around 20 inches long. The fish are polygynandrous (promiscuous), with both males and females having multiple partners.
Nassau groupers breed annually and engage in seasonal breeding. Reproduction is external, meaning the male’s sperm fertilizes the female’s egg outside her body. The spawning of Nassau groupers lasts eight days and begins on the full moon of December or January. The time to hatching ranges from 23 to 48 hours. There is no parental involvement in the raising of offspring.
Nassau Grouper Aggregate Spawning
Nassau grouper spawn once a year in aggregations — gatherings of hundreds, thousands, or tens of thousands. All of their known reproductive activity happens in these aggregations. They form at the edge of reef shelves in shallow water from November through February around the full moon, when water temperatures are around 26°C (79°F). [Sources: NOAA, Jordan Kime, Animal Diversity Web (ADW) /=]
As spawning time approaches, adults move from the reefs where they live to specific spawning areas. Some of them travel only a few kilometers; others are known to travel up to several hundred kilometers to the aggregation site. 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).
Spawning peaks three to five days after the full moon, but can continue up to eight days after. The timing and synchronization of spawning may be to accommodate widely dispersed adults, facilitate egg dispersal, or reduce predation on adults or eggs.
According to Animal Diversity Web: Nassau groupers aggregate to specific spawning sites on the full moon during December and January. This peculiar timing is of particular interest to scientists, who have suggested that, like other marine mammals, the gravitational pull of the moon at this specific time of year inspires migration to breeding grounds. Spawning aggregates can be as large as 100,000 individuals. They are strictly loyal to their spawning sites. This species changes its coloration when receptive to mating, usually becoming bicolor, darker, or incorporating a white belly. Dark coloration is though to be characteristic of males, while bicoloring and dark coloring typically correspond to submissive behaviors.
Nassau Grouper Development
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 larvae they are planktonic. As juveniles they are found in nearshore shallow waters in macroalgal and seagrass habitats. They shift deeper as they grow, to predominantly reef habitat (forereef and reef crest).[Sources: NOAA, Jordan Kime, Animal Diversity Web (ADW) /=]
Once fertilization occurs, eggs of Nassau groupers hatch within 48 hours. The larval period lasts 35 to 40 days, during which they are not recognizable as groupers. Nassau groupers reach sexual maturity between 4 and eight years of age. ("Synopsis of biological data on the Nassau grouper, Epinephelus striatus (Bloch, 1792), and the Jewfish, E. itajara (Lichtenstein, 1822)", 1999)
Fertilized eggs are buoyant and are less than a quarter inch wide. They hatch a day or two after being fertilized, and the pelagic larvae begin feeding on zooplankton after 2 to 4 days. After 1 to 2 months of floating with the ocean currents, the larvae settle in nearshore shallow waters in macroalgal and seagrass habitats. Little is known of their movements and distribution; they are rarely reported from offshore waters, and the link between spawning sites and settlement sites is not understood. We do know that they move into deeper and deeper water as they grow, toward offshore reefs.[Source: NOAA]
According to Animal Diversity Web: Nassau group mature slowly, reaching reproductive maturity between four and eight years of age (average five years of age). In captive populations, maturity occurs much sooner, which has been attributed to more abundant food sources and less environmental stress. In captivity, the average hatchling length of the notochord is 1.8 millimeters.
Endangered Nassau Grouper, Humans and Conservation
International Union for Conservation of Nature (IUCN) Red List categorizes the Nassau Grouper as Endangered; They have no special status according to the Convention on the International Trade in Endangered Species (CITES). The U.S. Endangered Species Act (ESA, U.S. Fish and Wildlife) lists them as threatened throughout their range in the Wider Caribbean Region: A ban was fishing Nassau groupers was put in place in 1992. Fishing regulations mandate fish must not be removed from the water, but rather the line must be cut. [Sources: NOAA, Jordan Kime, Animal Diversity Web (ADW) /=]
Overfishing has inflicted great damage on Nassau groupers. Both historical harvest and fishing at spawning aggregations have been identified as high-risk threats to Nassau grouper. They are targeted in spawning and non-spawning months, both at aggregation sites while migrating to or from those sites. Harvesting a species during its reproductive period increases adult mortality and diminishes juvenile recruitment rates (that is, the rate at which juveniles enter the fishery as adults). Both factors can greatly increase the risk of extinction for this species.[Source: NOAA]
Lack of effective regulations and enforcement is problem in regard to these groupers. There are many different regulations throughout Nassau grouper’s range. Their harvest is prohibited in the United States, while regulations elsewhere is limited. Some countries have no regulations in place to protect Nassau grouper. In some of the countries with protective regulations, there are too few enforcement officers to cover a large geographic area with many landing locations. Meanwhile, fish caught during closed season are held and later marketed as legal capture.
Nassau groupers were once considered the most economically important fish of the Bahamas Now they are regarded as an of ecotourism draw. In 1999, Nassau groupers brought $18 million to Florida from tourism and sport fishing. Fishing, however, has been limited in recent years do to their Endangered status. Nassau groupers appear to be good candidates for fish farming. Spawning can be induced in this species using human chrionic gonadotropin (HCG). The biggest obstacle is slow growth but the fish do grow faster in captivity than in the wild.
Image Sources: Wikimedia Commons; YouTube, Animal Diversity Web, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated March 2023