Squaretail Coralgrouper

 plectro_areolatusPhoto: John E. Randall

 

Plectropomus areolatus 

Description and Distribution

Head, body and median fins greenish grey to brown or brownish red, with numerous round to oval dark-edged blue spots (the largest about equal to a pupil); most spots are within a spot diameter of adjacent spots. The pelvic fins have dark brown to blackish membranes. The rear margin of the caudal fin has a white edge, often with a blackish submarginal band (1).

The squaretail coralgrouper is found in the Indo-Pacific from the Red Sea to the Phoenix Islands and Samoa, north to the Ryukyu Islands and south to Australia (2).

Preferred Habitat

This species inhabits lagoon and seaward reefs, especially areas with rich coral growth, and is most frequently encountered in channels along the reef front. It is found in a depth range of 1-20m.

Biology

Juveniles - No information.

Adults - The squaretail coralgrouper feeds exclusively on fishes. Often reaches 60 cm (3). The maximum length is 73 cm (4). Maturity size range is 31-35 cm TL (7).

Spawning aggregations

Spawning aggregations are known from the Solomon Islands, Palau; Pohnpei, Micronesia, Maldives, Australia, Kiribati, Fiji, Marshall Is., Indonesia, Tuvalu, and Samoa, amongst other locations.

One study showed that large numbers gathered in the seaward end of Ulong Channel, Palau, a few days before the new moon in May. The males displayed light bodies with about five irregular dark saddles and dark dorsal and anal fins (5).

Twice-monthly monitoring at sites in Komodo National Park, Eastern Indonesia, over five years, found aggregations typically formed during each full moon between September and February. Additionally, the squaretail coralgrouper occasionally aggregated during new moons between April and July (6).

Mariculture

No information; the species is not cultured.

Commercial Use

In Pacific countries it is one the most abundant and main target grouper species for the live reef fish food trade. It is sold in the Hong Kong live reef fish food market. Imports of the squaretail coralgrouper to Hong Kong were 2,319 tonnes in 1997. Common size at consumption is 38.24 - 50.21 cm TL (7).

In parts of Kiribati, local knowledge collected indicates spawning season from September to February with spawning peak occurring in early December. Fishing targeting spawning aggregations was traditionally practiced but became very intensive in the 1980's when an Outer island Fisheries Project was started which buys fish from the outer islands to sell in Tarawa, the capital. At the peak season of fishing during this time, an estimated catch of 2 tonnes of fish (about 1200 individuals) per day was normal (similar volumes are reported elsewhere and can represent a large proportion of fish aggregating at any one time). A UVC survey was conducted then which showed mean density of 0.13 individuals per 100sq.m and with mean TL of 40cms. In 2004 another survey was done at the same island, giving a mean density of 0.04 individuals per 100sq.m and mean TL of 33 cms (9).

Threats

Reports show declining stocks in Palau almost certain due to overfishing of aggregations. Before actual spawning around full moon, the species aggregates along outer reef channels and is responsive to baited hooks, making them very vulnerable to fishing; upward movements of some to take baited hooks has been mistaken for courtship or spawning behaviour. At least four grouper spawning aggregations have disappeared since the 1970s, and others are much reduced.

Conservation and Management

In Palau, the Marine Protection Act of 1994 and local traditional law prohibit sale or purchase of the squaretail coralgrouper from April 1 through July 31 each year, intended to protect spawning aggregation; however aggregations may extend into August, leaving fish unprotected at this time. In 1995 the Act was amended to prohibit any capture of these groupers even for subsistence purpose in the closed period (8).

In Australia, minimum size limits of 38 cm and a total combined daily bag limit of 7 coral trout apply to this species. Minimum size limits proposed for coral reef fin fishes are set at a point which allows at least half of the fish in a population to reach reproductive maturity and spawn before they are available for harvest; however, there is no indication that this is an appropriate size and longer lived species likely need much longer to replace themselves, on average, according to life history theory.

Conservation Status

In the IUCN (World Conservation Union) Red List, the species is included as ‘Vulnerable' because of the high demand and heavy pressure, thought to be increasing, on its spawning aggregations. Greatest catches of this species are taken at aggregations, being generally low at non-spawning times of the year.

Information Needed

Juveniles

References

(1) P.C. Heemstra and J.E. Randall. 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 ( Food and Agriculture Organization of the United Nations, Rome, 1993), 289pp.

(2) Fishbase website, www.fishbase.org.

(3) Heemstra and Randall, Loc. Cit. 1993 p. 289.

(4) Fishbase website, www.fishbase.org.

(5) Myers. 1989. Micronesian Reef Fishes. Coral Graphics.

(6) J,S. Pet, Peter J. Mous, A.H. Muljadi, Y.J. Sadovy and L. Squire. 2005. Aggregations of Plectropomus areolatus and Epinephelus fuscoguttatus (groupers, Serranidae) in the Komodo National Park, Indonesia: Monitoring and Implications for Management. In: Environmental Biology of Fishes 74(2) / October, 2005 .

(7) P.P.F. Lau and R. Parry-Jones, "The Hong Kong trade in live reef fish for food'' TRAFFIC East Asia and World Wide Fund for Nature, Hong Kong (1999)

(8) R.E. Johannes, L. Squire, T. Graham, Y. Sadovy and H. Renguul, ‘' Spawning aggregations of groupers (Serranidae) in Palau,'' The Nat.Conserv. Mar. Res. Ser. Publ. No. 1 (1999): 144 pp.

(9) Being Yeeting, 1999, unpublished report; Secretariat of the Pacific Community ProcFish data, 2005