Credit: Steve Lindfield
IUCN Red List Assessment VULNERABLE (2018)
Range Description: This species has a somewhat patchy distribution in the Indian Ocean where it is known from the Comoros, Red Sea, the Maldives, Chagos, the Laccadive Islands and Gulf of Mannar, the Andaman and Nicobar Islands, Myanmar and Thailand. In the Pacific, it occurs from the Philippines north to the Ryukyu Islands (Japan) and south to Indonesia, Australia (northern Western Australia and Queensland), Papua New Guinea, the Solomon Islands and most of Micronesia. Its depth range is 1-70 metres (for map and countries see IUCN Red List Assessment).
Species Summary: This coral trout is widely distributed around shallow coral reefs in lagoons and seaward coral-rich areas. The species may be a protogynous hermaphrodite that starts its life as a female and then later changes sex to become a male, but this has not yet been confirmed. Size of sexual maturation is about 2-3 years old (at 35-40 cm TL) and the species can live 12-14 years and reach 70 cm TL. The species feeds on exclusively on fishes.
Credit: Ebill Cam
As for many other medium to large-sized groupers, the squaretailed coral trout aggregates to spawn, its only known mode of reproduction. Healthy aggregations of many hundreds to a few thousand fish are known. The seasonal and lunar timing of aggregation formation and spawning is highly predictable in specific locations but varies across the geographic range of the species. Spawning occurs just before new moon in Palau, Solomon Islands, Papua New Guinea and the Seychelles, and just prior to the full moon in Pohnpei and Fiji. Some workers have suggested that not all aggregations or groupings of this species are associated with spawning, highlighting the need for workers to be aware of spawning-related behavior and to look for the presence of gravid (ripe with eggs) females. Groups of small fish, for example, sometimes roam around spawning sites and these may be juveniles or small females learning about the aggregation site.
Squaretail coralgrouper aggregations overlap somewhat spatially and temporally with those of camouflage grouper (Epinephelus polyphekadion) and brown-marbled grouper (Epinephelus fuscoguttatus) but when aggregations occur in depths of greater than 12-15 metres, this species is typically found in shallower areas than the other two species which can make them particularly susceptible to spear-fishing. The species can undergo many colour changes from black or yellowish females to striped or light-coloured males.
Fisheries: The species is one of several medium to larger groupers taken regularly in coastal reef fisheries in much of its range and is valued in the international live fish trade in SE Asia, fetching a high price at retail. It has been part of this trade for several decades but there has also recently been growth in the international marketing of chilled/frozen fish, for example out of Indonesia and the Maldives, as demand for groupers increases. Fish sizes in trade can be quite small, with more and more juveniles being sold. To supply commercial trade, spawning aggregations are sometimes heavily targeted by fishers. Due to overfishing, the squaretailed coral grouper is declining in some areas and is listed as threatened globally (Vulnerable) on the IUCN Red List (2018).
Credit: Jack Randall
Management/Conservation: Despite declines and its threatened status, the squaretailed coral trout receives little management or conservation protection in much of its range. Exceptions include protection of some of its spawning aggregations and minimum size measures to protect juveniles and allow them to reach reproductive size and age. For example, sales (Pohnpei, Palau) and catch bans (Palau, Fiji, Solomon Islands) are in place during all or most of the reproductive season. No-take protected areas specific to spawning aggregation sites are in place in Palau, Pohnpei and the Solomon Islands. The Maldives has introduced minimum capture and trade sizes for the species. In the Great Barrier Reef Australia, this species is managed with no-take marine protected areas, size and catch limits and seasonal spawning closures.
Key Recent Publications on biology, trade, fisheries and management: for earlier publications, please refer to IUCN Red List Assessment and https://www.springer.com/gp/book/9789400719798
FISHBASE; http://www.fishbase.org/summary/Plectropomus-areolatus.html
Hamilton, R.H., Potuku, T. and Monambault, J.R. (2016). Community-based conservation results in the recovery of a reef fish spawning aggregations in the Coral Triangle. Biological Conservation 144, 1850- 1858
Hughes A. T, Hamilton R. J, Choat J. H, Rhodes K. L (2020) Declining grouper spawning aggregations in Western Province, Solomon Islands, signal the need for a modified management approach. PLoS ONE 15(3): e0230485.
Khasanah, M., Sadovy de Mitcheson, Y., Kadir, N. N. & Jamaluddin J. (2020). Management of Grouper Export Trade in Indonesia Reviews in Fisheries Science & Aquaculture; 10.1080/23308249.2018.1542420
Ma, K. Y., van Herwerden, L., Newman, S. J., Berumen, M. L., Choat, J. G., Chu, K. H. and Sadovy de Mitcheson, Y. (2018). Contrasting population genetic structure in three aggregating groupers (Percoidei: Epinephelidae) in the Indo-West Pacific: the importance of reproductive mode. BMC Evol Biol. 2018; 18: 180. doi:10.1186/s12862-018-1284-0. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6278153/
Rhodes, K.2018. Plectropomus areolatus. The IUCN Red List of Threatened Species 2018: e.T64411A100466794.
Rhodes, K.L., Taylor, B. M., Wichilmel, C.B., Joseph, E., Hamilton, R. J., and Almany, G. R. (2013) Reproductive biology of squaretail coralgrouper Plectropomus areolatus using age-based techniques. J. Fish Biol. 82, 1333–1350
Rhodes, K.L., Nemeth, R.S., Kadison, E. and Joseph, E. (2014). Spatial, temporal and environmental dynamics of a multi-species spawning aggregation in Pohnpei, Micronesia. Coral Reefs 33: 765-775.
For current perspectives on live reef fish trade in Southeast Asia, there are two recent publications:
Online visual sources:
https://www.youtube.com/watch?v=O8Doh_ro3V0 courtship of squaretailed coral trout
Lakshadweep, India; footage of spawning aggregation: https://www.youtube.com/watch?v=1uJqHQv8ju8