Photo: John E. Randall
Description and Distribution
The coral trout, otherwise known as the leopard coral grouper, is distributed across the western Pacific from southern Japan to southern Queensland, west to Lombok, Indonesia and Western Australia, and east to Caroline Islands and Fiji; occurring at depths of 3 to 100m. It is listed as near threatened in the IUCN red list (Assessed in 2004). Plectropomus leopardus is a medium-sized diurnally active grouper easily observed underwater, therefore vulnerable to spear fishing but also amenable to accurate visual census surveys. They can live up to 14-19 years with maximum length reaching 63.0 FL (female) and 74.6 FL (male) (4,5,8,11,12,24,30).
The larvae are pelagic; juveniles live in demersal shallow water in reef habitats, especially around coral rubble, whereas adults inhabit coral reefs (2,11,25).
The above diagram shows the range of the coral trout (highlighted in green)
and reported spawning aggregation sites (highlighted in red)
P. leopardus grows rapidly in the first 2-3 years of life, and matures relatively early. As juveniles their diet consists largely of benthic crustaceans, but this shifts just prior to maturity to a piscivorous diet. Recruitment of juveniles appears to be largely driven by current patterns and geomorphology. P. leopardus is a protogynous hermaphrodite, maturing as female first and then changing to male at around 7 years. The operational sex ratio (F:M) largely varies with location and exposure to fishing - ranging from 0.9 to 5.5 (1,2,3,8,12,25, 28).
The mating patterns of P. leopardus illustrate a relatively complex and flexible reproductive strategy compared with other serranids of similar size. The high spawning frequency and high annual fecundities, at least double those of other serranids, may be the reason why P. leopardus is a relatively abundant serranid and is perhaps more resistant to fishing pressure (5,7,9,16,21,23).
On the northern GBR, P. leopardus forms well defined, spatially and temporally predictable spawning aggregations at the same sites over years. Aggregations form for a five day period around the new moon over three months during Austral spring to early summer. Pair spawning in aggregations is confined to a 30 minute period at sunset. However, only around 20% of individuals appear to participate in aggregation spawning. Further, around 50% of all spawning occurs outside aggregations including those happened during the first quarter lunar phase (3,9,10,20,27).
The generic group coral trout, which comprise three main species (leopardus, laevis and maculatus), and four lesser species, are the major commercial finfish taken in Australia, predominantly on the Great Barrier Reef (GBR). Commercial log books do not distinguish the Plectropomus species, but independent research shows that leopardus comprises 80% of the Plectropomus commercial catch. It is also the most abundant of the Plectropomus species on the GBR (10).
Commercial log book data show significant increases in catch and effort of Plectropomus spp. on the GBR. In 2000 the commercial harvest was worth AUS$ 15.5 million. P. leopardus is also taken on the GBR by private recreational fishers and by a commercial charter fishery for recreational fishers. P. leopardus is also taken commercially and recreationally from the Houtman Albrolhos islands in Western Australia (WA). The WA fishery is managed through minimum size limits, recreational bag limits and area closures and is not considered overexploited. Artisanal fisheries for P. leopardus exist in the Pacific Islands where they occur, namely Fiji, Papua New Guinea, New Caledonia and elsewhere in Southeast Asia (15,25).
In the mid 1990s the trade in live P. leopardus, primarily to Hong Kong, grew in Australia and the Philippines and the portion of live fish in the commercial catch grew to around 25%. By 1998 live coral trout fetched up to eight times the price of whole or filleted coral trout. The export of live P. leopardus has been a significant commercial fishery in the Asia-Pacific region, with fish taken primarily from Indonesia and Philippines. Imports into Hong Kong increased by 58% from 1999 to 2002, coming largely from Australia and Philippines as other countries' exports declined. Although the majority of P. leopardus in Hong Kong live fish markets are above size at first reproduction, capture of juveniles and grow out is practised, particularly in the Philippines (11).
Commercial fishers in Australia use simple hook and line, generally with one hook, with frozen pilchard as bait, fishing from small tender boats to a mother vessel. Recreational fishers use handlines, rods and spearguns. Mother vessels have large freezer capacity and may stay out for 3-4 weeks. Artisanal fisheries in Fiji and New Caledonia take P. leopardus by hook and line and spear gun, and incidentally by trap and net. Some are kept live for the live fish trade. In the Philippines, fish are caught by hook&line and by cyanide solution (24)
P. leopardus is a high-valued and much sought-after grouper species. Some 2000 tonnes of this species are imported to Hong Kong, the major trade centre, from countries like Australia, Indonesia, Malaysia, Vietnam, and the Philippines. The retail price of the species in Hong Kong and mainland China ranges from 50-70USD/kg in 2002 (19).
P. leopardusis a popular candidate for mariculture in Asia-Pacific region - the collection of wild broodfish, application of hatchery and grow-out husbandry (17, 29).
Coral Trout in Fish Tank
Photo: Yvonne Sadovy de Mitcheson
There is no strong evidence of targeted fishing of spawning aggregations of P. leopardus on the GBR. However, the potential for increased catchability due to P. leopardus moving from habitats inaccessible to fishers to regularly fished areas while migrating to aggregations has been demonstrated through simulation. The collapse, recovery and further collapse of one spawning aggregation in the Cairns region of the GBR was attributed to commercial fishers targeting this site. It is likely that easily located aggregation sites are vulnerable to targeted fishing but the relatively small aggregations and several aggregations per reef of P. leopardus makes it less vulnerable than other groupers. No intentional targeting of spawning aggregations is reported from the Torres Straits (13,14,30,32)
Aggregation fishing is known from the Asia- Pacific region in connection with the live fish trade to Asia. The extent to which this targets P. leopardus aggregations is not known. However, aggregation fishing for live groupers in Indonesia has been so great that severe declines in catches were experienced and these are likely to include P. leopardus. Most studies and conservation action in the Asia-Pacific region have focussed on Plectropomus areolatus, and there is little known or discussed of P. leopardus, except in Australia (9,27).
In the Philippines, large number of sub-adult sized fish are put into net cage and grown-on to market-size. This practice, if not managed carefully could lead to recruitment overfishing and growth overfishing (19).
Conservation & Management
Conservation and management action is largely limited to Australia where the commercial Queensland fishery is limited entry, licensed, with gear restrictions and a minimum size limit of 36cm FL. The size limit prevents fishing of the first three cohorts, representing both the fastest growth period as well as when females start reproducing. Recreational fishers are limited to 10 coral trout per person. Charter fishing operators are regulated by permits & bag limits.
The Queensland reef fishery operates within the GBR Marine Park with area closures where fishing is prohibited. Studies on the impacts of these closures on P. leopardus reveal complex results, but generally females are larger, older and more abundant on closed reefs suggesting reef closures are an effective strategy against fecundity limitation. Despite extensive fisheries and protected area controls, significant declines in P. leopardus abundance in the central and southern sections of the GBR are reported. This observation together with the decline in catch rate since the early 1990s, has led to reviews and revision of legislation. In 2002 the Queensland Fisheries Service introduced three 10 day closures (around the new moon) (reduced to 2 days in 2009) to protect spawning aggregations of key target species but designed primarily to protect P. leopardus aggregations and migrations. Meanwhile the management authority completed a massive re-zoning of the park in 2004, resulting in 33% of the Park being closed to fishing.
The Houtman Albrolhos Islands in WA have been declared a Fish Habitat Area (FHA) by the Department of Fisheries. Seventeen percent of the FHA was closed to fishing in 1994. After eight years of closure P. leopardus densities increased 3-7 fold which was attributed to reduced fishing mortality and their relatively small home ranges. No information is reported on their spawning aggregations in WA.
The status of P. leopardus populations in Pacific Island countries and the role aggregation fishing plays in the export fishery for live fish is largely unknown. Volumes of catches of high value groupers in the live trade from Indonesia, Malaysia, Cambodia and Vietnam have plummeted while imports to Hong Kong continue to rise.
Because P. leopardus aggregations are relatively small, there are several per reef and aggregation spawning contributes relatively little to the total reproductive output, management and conservation of P. leopardus in Australia is probably best focussed on the species in general. However, in the Philippines, Indonesia and Fiji where substantial trade in live coral trout occurs, complete protection of spawning aggregations through seasonal closures is likely to be a more important measure. In the Philippines a management plan is being developed for Palawan (Sadovy pers comm).
Biological and ecological studies of P. leopardus from across its range, particularly from the Indian Ocean, Philippines, Fiji, Japan and Indonesia; data on species-specific abundance, catch and effort in the artisanal fisheries of the Pacific Islands to properly assess the population status of this species; knowledge of reproductive parameters and spawning behaviour of populations; monitoring of aggregations and of the impacts of spawning closures as part of fisheries management.
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