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Marine Animal Encyclopedia

Nassau Grouper Epinephelus striatus

Who?

Species ID: S.ESb

Description: A large, deep-bodied fish with rounded fins and prominent dorsal spines, often with yellow tips. The body is covered in wide bars that appear green to brown on a pale background, and a large black saddlespot appears at the base of the tail. These fish can pale, darken, or adopt specific body patterns at will. Sexes appear similar and juveniles resemble adults

Maximum Size: 1.2 m (4 ft)

Longevity: Approximately 30 years

Status: Endangered according to the IUCN endangered species list

Nassau Grouper & People: Nassau grouper were once the most important food fish in the Caribbean, but severe overfishing and exploitation of vulnerable breeding aggregations has contributed to a population decline of roughly 60% in the past 30 years. Harvest and sale of Nassau grouper is now banned in several countries in an effort to help the population recover, but their numbers continue to decline in many areas

Where?

Geographical Range: Occasional throughout the Caribbean, but rare in the Gulf of Mexico

Coral Reef Zone: Nassau grouper can be found in rocky areas of the back reef, fore reef, and drop-off zones

Favourite Habitat: Nassau grouper prefer areas with caves and crevices which they use for shelter

Depth Range: 6–30 m (20–100 ft)

A Day in The Life

Dawn: Feeding activity increases when low light levels help grouper approach prey

Day: Grouper wander the reef and may feed

Dusk: Feeding increases; spawning occurs at this time during the breeding season

Night: Grouper rest among rocks; some feeding may occur

Who Eats Who?

Nassau grouper are eaten by only the largest reef predators such as sharks, barracuda, and larger groupers, including members of their own species! Nassau grouper themselves are one of the larger coral reef predators and consume most reef inhabitants that can fit into their mouth, especially fish, crabs and lobsters.

Scuba Diver & Snorkeler Best Practices

Don’t buy souvenirs made from marine organisms Never purchase souvenirs made from marine organisms, such as corals and turtles; it is environmentally damaging and often illegal.

Approach

Nassau grouper are curious individuals and generally easy to approach, in fact, they often come close to examine divers and snorkelers. However, in areas where they are hunted by spearfishers, these groupers stay far away from humans.

Feeding Behaviour

Nassau grouper are carnivorous ambush predators. They lie in wait among the reef substrate, using their camouflage abilities in the low light of dawn and dusk to avoid being seen by their prey. When prey species come too close, the grouper pounces from hiding and engulfs them. Nassau and other groupers create a strong sucking force, by opening their mouths rapidly, which is very effective at pulling the prey into their jaws and also helps  them in pulling prey out of reef cracks and crevices. On other occasions, Nassau grouper actively seek out prey on the reef, and have even been seen stirring up the sand with their tail to uncover burrowing prey such as crustaceans, jawfish, and garden eels.

Observe, record & share:

O S.ESb-101 – Ambush: Grouper lunge forward and engulf nearby prey from hiding, using a powerful sucking force to draw prey into their mouths

O S.ESb-102 – Digging: Grouper beat their tails near the bottom to stir up sand and uncover buried prey

Attack & Defense Behaviour

Nassau grouper are solitary fish and defend a territory against other Nassau groupers. During a territorial dispute, which usually involves chasing, smaller grouper often adopt a submissive bicolour pattern consisting of a dark back and pale belly with a white stripe running through the eye. Although they are one of the reef’s largest predators, they are still a prey species for larger grouper and sharks. When predators are nearby, Nassau rouper settle into the reef and rapidly pale or darken to camouflage themselves. If confronted, Nassau grouper can produce a variety of loud booming sounds, created by vibrating the swim bladder, in an attempt to intimidate predators.

Observe, record & share:

O S.ESb-201 –Chasing: A resident Nassau grouper chases away intruders into its territory, often with an open mouth and spread fins

O S.ESb-202 – Submissive pattern: Fish exhibit a dark back and pale belly with a pale stripe running across the eye to indicate that they do not wish to fight

O S.ESb-203 – Camouflage: Nassau grouper rapidly pale or darken to blend into the reef and hide from passing predators

O S.ESb-204 – Sounds: Nassau groupers produce loud booming sounds, which are used to frighten away predators, by vibrating the swim bladder

Reproductive Behaviour

Nassau grouper reproduce sexually by broadcast spawning in open water. Some scientists believe that they change sex as they age, like other grouper, but this issue is still hotly debated. The most recent research suggests that juveniles must pass through a non-reproductive bisexual phase before maturing into either a male or female. During the breeding season, in the days leading up to the full moon, thousands of Nassau grouper migrate to traditional spawning grounds. Groups often form in deeper water, near reef spurs or drop-offs facing the open ocean, and mating activities persist for about a week. Prior to spawning, most fish adopt the submissive colour pattern described previously. As dusk approaches, females that are ready to spawn become uniformly dark and are chased by several males. Small schools periodically break away from the main aggregation and rush towards the surface where they release eggs and sperm. The breeding season of Nassau grouper typically extends from November to December, with the spawning aggregations reaching their peak size, in terms of number of individuals, two days after the full moon.

Observe, record & share:

O S.ESb-301 – Spawning aggregation: Fish form groups near drop-offs facing the open ocean

O S.ESb-302 – Submissive pattern: Males adopt the submissive colour pattern described earlier, signaling a suspension of aggression during spawning

O S.ESb-303 – Dark females: Females ready to spawn adopt a uniformly dark pattern

O S.ESb-304 – Group spawning rush: Fish rush towards the surface where eggs and sperm are released

Highlight Behaviours

Spawning aggregations: Many complex behaviours and colour patterns can be observed at Nassau grouper spawning sites. During the day, spawning grouper remain close to the seafloor and retain their normal striped colour pattern to remain camouflaged from predators. As dusk approaches, the fish move higher into the water column and both males and females may adopt the submissive bicolour pattern indicating a non-aggressive attitude during spawning in this normally territorial fish. Females ready to spawn change from a bicolour to a uniformly dark colouration. Dark females lead a small group of males, still wearing the bicolour pattern, high into the water column where they release gametes simultaneously before returning to the main group. Additionally, some ripe females may adopt a uniformly pale colour phase, possibly for improved camouflage over sandy bottoms, before turning dark to spawn. The complex colour changing of Nassau grouper is the subject of much current research, in order to learn more about this fascinating creature.

Did You Know?

• Some Nassau grouper spawning sites are known to have been active for as long as 50 years.

• Of the 60 to 80 Nassau grouper spawning sites discovered to date, roughly half have already been fished to the point of collapse. Once extinguished, there is no evidence to show that spawning aggregations ever re-form, since young fish are thought to learn their locations from experienced adults.

• Nassau grouper are frequent customers at cleaning stations, where juvenile reef fish, gobies, and shrimps remove parasites that cling to the skin and gills of their clients.

What to do?

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Nassau Grouperzoom image
  • Order Serranidae
  • Length 1.2 m (4 ft)
  • Weight Not recorded
  • Depth 6–30 m (20–100 ft)
  • Habitat Found in the rocky areas of the back reef, fore reef and drop-off zones
  • Distribution Throughout the Caribbean
Nassau Grouper habitat mapzoom image