Surge grouper (Epinephelus socialis)

Surge grouper among coral
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Surge grouper fact file

Surge grouper description

GenusEpinephelus (1)

Well adapted to its rough, oceanic environment, the surge grouper (Epinephelus socialis) is a large, sturdy fish with a strong, stout body and rounded head and tail (2). Generally whitish on the head and body, the surge grouper is covered in small, close-set blackish-brown spots which join together towards the tail to form wavy, irregular bands. However, the throat and underside lack spots. Four dark blotches are visible on the back, with an additional blackish, saddle-shaped blotch at the base of the tail. The spots which pattern the body of the surge grouper tend are bigger in juveniles, and become smaller as the fish grows (2) (3) (4).

The fins and tail of the surge grouper are similar in colour to the body at the base, becoming darker greyish-brown towards the tips. The dorsal, caudal and anal fins are covered in small, white spots, usually with a black band just before the tips and often have a white margin. The fleshy pectoral fins have white spots and a white margin at the tips, and the pelvic fins are white at the front and dark greyish-brown elsewhere (2) (3) (4).

Serranus socialis.
Merou Houleux.
Mero Oleado.
Length: up to 52 cm (2)

Surge grouper biology

A voracious predator, the surge grouper spends the majority of its time close to the sea bed, ambushing and feeding on bottom-dwelling crustaceans, octopuses and small fish (1) (2) (4).

Although very little is known about the biology of the surge grouper, it is likely that the species may aggregate and spawn for short periods, and at the same location each year (5).


Surge grouper range

The surge grouper is found around oceanic islands in the Pacific Ocean, including the Ogasawara Islands, Marcus Islands, Mariana Islands, Marshall Islands, Phoenix Islands, American Samoa, Cook Islands, Line Islands, Society Islands, Rapa, Tuamoto Islands, and the Pitcairn Group (1) (2) (3) (4).


Surge grouper habitat

Restricted to a very specific habitat, the surge grouper is found only in the shallow parts of coral reef flats and channels which are exposed to wave action from the ocean. It typically occurs at depths of less than 3 metres (1) (3). The surge grouper is most common on atolls (circular coral reefs surrounding a lagoon), although juveniles and occasionally adults are sometimes collected from tide pools (2) (4).


Surge grouper status

The surge grouper is classified as Near Threatened (NT) on the IUCN Red List (1).

IUCN Red List species status – Near Threatened


Surge grouper threats

The surge grouper is threatened mainly by subsistence fishing (1). Although its population size is unknown, the surge grouper is not thought to be very abundant, and populations are likely to be highly fragmented. Because the surge grouper is a large fish which lives in shallow reef habitats that are usually easily accessible, it is considered an easy target for hunting throughout much of its range. It is particularly vulnerable around islands with high human densities (1) (5).

Pollution of shallow oceanic reefs and coastal development is also causing increasing degradation of the surge groupers important coral reef habitat (1).


Surge grouper conservation

Although there are no known conservation measures which are targeted specifically at the surge grouper, it is likely that this species will benefit in marine reserves where the reef habitat is protected (1).

Further research is needed on the abundance, distribution, reproduction and life span of the surge grouper, while measures are also needed to manage fisheries which target this species (1). With marked declines seen in many grouper species, the IUCN/SSC Grouper and Wrasse Specialist Group is currently assessing the threat levels to this group of important fish, and is developing Action Plans and activities to increase awareness of and reduce risks to these threatened species (5).

ARKive is supported by OTEP, a joint programme of funding from the UK FCO and DFID which provides support to address priority environmental issues in the Overseas Territories, and Defra

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Anal fin
In fish, an unpaired fin on the under surface of a fish, behind the anus.
Caudal fin
The tail fin of a fish.
Diverse group of animals with jointed limbs and a hard chitinous exoskeleton, characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps and barnacles.
Dorsal fin
The unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans.
Pectoral fins
In fish, the pair of fins that are found one on each side of the body just behind the gills. They are generally used for balancing and braking.
Pelvic fins
In fish, the pair of fins found on the underside of the body.
The production or depositing of large quantities of eggs in water.


  1. IUCN Red List (February, 2011)
  2. Heemstra, P.C. and Randall, J.E. (1993) FAO species catalogue.Vol.16. Groupers of the world (Family Serranidae, Subfamily Epinephelinae). An annotated and illustrated catalogue of the grouper, rockcod, hind, coral grouper and lyretail species known to date. FAO Fisheries Synopsis No. 125, Vol. 16. Food and Agricultural Organisation of the United Nations, Rome. Available at:
  3. Cook Islands Biodiversity and Natural Heritage – Surge grouper (Epinephelus socialis) (February, 2011)
  4. FishBase – Surge grouper (Epinephelus socialis) (February, 2011)
  5. IUCN/SSC Groupers and Wrasses Specialist Group (February, 2011)

Image credit

Surge grouper among coral  
Surge grouper among coral

© Marc Chamberlain / Inc.
77-6425 Kuakini Hwy.
Ste C2-200
Kailua Kona,


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