P. Labrosse

The humphead wrasse, Cheilinus undulatus: Synopsis of a threatened and poorly known giant coral reef fish

The humphead wrasse, Cheilinus undulatus, is the largest living member of the family Labridae, with a maximum size exceeding 2 m and 190 kg. Its geographic range covers much of the Indo-Pacific. The species is not common, recorded maximum adult densities rarely exceeding 20 fish/10,000 m2. Small individuals are typically associated with high coral cover; larger fish are found mainly on outer or deep reefs, steep slopes and passes, singly or in small groups and seagrasses. However, for reproduction the species forms small spawning aggregations of tens to more than one hundred fish. The diet of the humphead wrasse includes large invertebrates and small fishes. The species attains at least 30 years and reaches sexual maturation at about 35–50 cm total length and <5 years of age. Most small adults are female while mainly males exceed 1 m and there is evidence of female to male sex change. The humphead wrasse is of considerable cultural value in some Pacific countries and is among the most prized in the live reef food fish export trade, for which it is often taken in its juvenile size range, either directly for sale or, increasingly, for grow-out to market size. It is also marketed chilled. The species is particularly sensitive to fishing pressure. In most fished areas, density and body size have dropped substantially. It appears to be particularly heavily targeted and depleted in SE Asia and in some places faces extirpation. The humphead wrasse is often taken by night spearfishing and by cyanide, with protection typically weak or non-existent, despite regulations and by a ‘vulnerable’ assessment on the 1996 IUCN Red List. The humphead wrasse has not been reared successfully in hatcheries. Other giant reef fish share many similar problems and detailed study of the humphead wrasse contributes to a better understanding and conservation of all such species. This review examines and evaluates published and gray literature, original unpublished research and correspondence with almost 50 knowledgeable workers. It examines the value of such sources for quickly, but adequately, assessing the conservation and management status and key data gaps in species that are little known, vulnerable, difficult and expensive to study and may require urgent management or conservation action.

Spatial structure of commercial reef fish communities along a terrestrial runoff gradient in the northern lagoon of New Caledonia

The spatial distribution of commercial reef fishes from four areas of the northern lagoon of New Caledonia was studied following a terrestrial runoff gradient ranging from very low on the western barrier reef to high on the northern fringing reefs. Species richness decreased from eastern reefs (30.4 species transect-1) to northern fringing reefs (21.4), suggesting a link between terrestrial influence and species richness. Density ranged from 0.49 fish m-2 (western reefs) to 0.69 fish m-2 (eastern reefs), but did not show any particular trend. Biomasses increased from 148 g m-2 on the northern fringing reefs to 447 g m-2 on the western reefs. Such high values are likely due to the very low fishing pressure in the whole area. Numerous significant relationships were found between fish descriptors (i.e. diversity, density, biomass and mean weight) and terrestrial influences (i.e. distance to coast, visibility, % of carbonates in the sediment, % of mud, granulometry and color of sediments). Descriptors of total ichthyofauna were all positively correlated with decreasing terrestrial influence. The 6 dominant fish families displayed similar trends and were positively correlated with decreasing terrestrial influence, except for Siganidae which showed the opposite trend. Some of the most common species, such as Scarus sordidus and Siganus doliatus, had no particular distribution pattern. Size, density and biomass of other species, such as Lethrinus atkinsoni, Cheilinus undulatus, Hipposcarus longiceps, Scarus microrhinos and Acanthurus xanthopterus, were significantly correlated to parameters characteristic of offshore reefs. Conversely, Plectropomus leopardus, Scarus ghobban and Siganus lineatus were closely related to coastal reefs. Some species had significant correlations with parameters characteristic of intermediate reefs, such as Scarus schlegeli and Acanthurus nigricauda. Data for Plectropomus leopardus and Scarus ghobban suggested a possible ontogenic migration of these two species from the northern fringing reefs, where numerous small individuals were observed, to offshore barrier reefs, where only large individuals were recorded.

Fish stock assessment of the northern New Caledonian lagoons : 2 – Stocks of lagoon bottom and reef-associated fishes

Fish stocks found on lagoon bottoms and near reefs are characterized by a high diversity and heterogeneous habitat which make stock estimation difficult. In particular, it is necessary to combine several methods in order to evaluate the major components of these stocks. The present study aimed at estimating reef fish stocks in the Northern Province of New Caledonia, a region where they represent a major target for the local fishermen. These estimates were based on experimental fishing with handlines and bottom longlines. Handlines were used to assess the stocks near reefs, and longlines for those in areas away from reefs and on lagoon soft bottoms. Handline stations (363) were sampled in three different regions (west, north and east lagoons) and three biotopes (nearshore, middle lagoon and barrier reef). A total of 104 species were caught, the major families being Lethrinidae, Lutjanidae and Serranidae. Species composition and catch per unit of effort (CPUE) varied among regions and biotopes. In particular, the north zone showed characteristics of an unexploited area with very high yields. An increase in CPUE and fish size from the coast towards the barrier reef and with increasing depth was observed in all regions. Correlations between CPUE from handlines and the numerical density and biomass estimates from underwater visual censuses (UVC) performed on nearby reefs were significant. A total of 206 longline stations were sampled in the west and east regions. A total of 80 species were caught, the major families being the same as those caught in stations with handlines with the addition of Carangidae. The CPUE of longlines was significantly correlated with numerical density and biomass estimates made by UVC along the longlines. Stock estimates based on the correlations between CPUE from handlines or longlines and UVC estimates indicate that 90 % of the lagoon stock were found on soft bottoms and near reefs. Reefs, despite biomasses that were five times larger than soft-bottom and near-reef areas, made only a small contribution to total stock. The ratio between density and CPUE was highest for the lowest densities, thus indicating that fishing efficiency increased with density. Comparison of handline catch performed around reefs and UVC data from nearby reefs suggests that there were strong relationships between the fish assemblages of these two biotopes.

Commercial fish assemblages on New Caledonian fringing reefs submitted to different levels of ground erosion

Abstract A comparative study was conducted in two zones of the Northern Province of New Caledonia, one located windward (east coast) and the other located leeward (west coast). In each zone, three major sectors were investigated: fringing reefs close to areas of important mining activities, fringing reefs close to areas of moderate mining activities, and fringing reefs close to areas free of mining activities. In addition, on the west coast, fringing reefs close to areas of high natural ground erosion were also studied. Only commercial fish species sensus lato were censused on a total of 163 stations, concerning 165 fish species. Substrate characteristics were not different between zones and sectors. However, significant differences were observed for living organisms: live coral cover was higher in non-mining sectors than in mining ones, and algal cover increased with increasing mining activities. The three main descriptors of the commercial fish communities (e.g. mean species richness, density and biomass) have all shown lower values in sectors submitted to the lowest ground erosion levels, although these trends were not all statistically significant. Similar results were found for some of the major fish families, such as the Acanthuridae and Siganidae, whereas other families had no specific pattern, such as the Lutjanidae, or a ‘partial’ pattern (i.e. on only one coast), such as the Serranidae, Lethrinidae, Mullidae, Labridae and Scaridae.