Reef finfishing pressure risk model for Pacific Island countries and territories

A reef finfishing pressure risk assessment model was developed to predict the status of reef and lagoon fisheries in terms of the current likelihood for sustainable or unsustainable finfishing for any given rural coastal community and its associated reef area in the Pacific Island countries and territories (PICTs). The prediction model aimed at developing a robust system that allows planners to confidently classify any coastal rural site within PICTs with a minimum and relatively easy-to-obtain dataset as being exposed to four classes of low to high finfishing pressure. This model is a response to limitations on data regarding current resource and user status in PICTs that make it difficult to ascertain fish supply for food security and livelihood of coastal communities. The model is based on the latest reef productivity scenarios developed based on a global review of currently known landing data and ecological footprints, reported likelihood of reduced reef productivity in PICTs due to ecological and human factors, and the use of current finfish catch rates collected as a proxy for fishing pressure. The prediction model was developed on the basis of a regional dataset including 63 study sites in 17 PICTs using linear discriminant analysis. The smallest feasible model with a leave-one-out error rate of 14.3% demands nine input variables that can be easily obtained and require only a minimum survey effort. Statistically significant response of decreasing fish length in six fish families important to artisanal fisheries in PICTs (Acanthuridae, Lethrinidae, Mullidae, Scaridae, Serranidae and Siganidae) to increasing catch rates or increasing fishing pressure proxies was used as an independent external factor to validate our hypothesis and the model developed. The reported catch length for Acanthuridae, Scaridae and Serranidae was statistically significantly different between the four finfishing pressure risk groups defined. Due to the lack of data on the natural status and productivity of the coral reefs in question and their historic use, care should be taken in interpretation of current catch rate figures. Classification of sites at low current finfishing pressure risk may reflect catch rates that are adapted to low stocks, either caused by previous depletion or due to natural unfavorable conditions. At the same time, sites classified as being at potentially high finfishing pressure risk may indeed be subject to current overfishing, but may as well feature high natural stock and productivity assets that allow for higher catch rates than elsewhere.     

Fish stock assessment of the northern New Caledonian lagoons:3 – Fishing pressure,potential yields and impact on management options

The potential yields of demersal reefal and lagoonal finfish, which are valuable for trade or consumption in the Northern Province of New Caledonia, are unknown. Fishing pressure was estimated from tally-sheets of professional fishermen to assess trade fishing and a household consumption survey to assess subsistence fishing. Total yield was estimated to be 1 326 tonnes in 1995, 94 % of which correspond to subsistence fishing. Most of the catches were taken from the east and west coasts; in the north zone (Bélep Archipelago) catches were very low. From this fishing pressure and the total stock values, the maximum sustainable yield (MSY) was estimated to be 12 600 t, which was about 10 % of the total stocks assessed in the Northern Province (138 300 t). This MSY was dominated by five families, namely Lethrinidae, Acanthuridae, Scaridae, Serranidae and Lutjanidae. The results suggest that fishing effort in the Northern Province of New Caledonia could increase without endangering the stock. However, on a smaller geographical scale, some locations (Koné and Népoui on the west coast), reef habitats (near-reef areas) or species groups (fish caught by line) were already being intensively fished. Fishing techniques should be diversified so that part of the fishing effort be redirected toward the least heavily exploited groups of species and biotopes.     

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.     

The reef fisheries surrounding the south-west coastal cities of Madagascar

The artisanal fishery in south-west Madagascar, around the coastal cities of Morondava, Morombe and Tuléar, is particularly active. In the Morombe and Tuléar regions, fishing pressure focuses on coral formations close to landing sites and reef fish constitute the main part of the catch (Lethrinidae, Haemulidae, Siganidae). In Morondava, fishing is practised very close to the shore on sandy substrates, but also on offshore reef shallows. The catches are more diverse and made up of reef fish (Serranidae, Lutjanidae) and non-reef species. Fishing from Morondava targets the highest trophic level of the coral reefs (piscivores/macroinvertebrate feeders: 87% of the catch) whereas in Tuléar and Morombe the higher fishing effort means that lower trophic levels are targeted to maintain catches. Despite the high fishing effort, especially around Morombe and Tuléar (standardizing fishing effort of 5200 hook h km^–2 year^–1 and of 12 300 hook h km^–2 year^–1, respectively), the catch per unit effort (CPUE) is still relatively high; it varies from 0.6 to 2 kg h^-1 per person over the whole zone and seems to be more linked to the fishing method used and to the degree of professionalism than to variations in the abundance of the resources surrounding the three cities. The relatively high CPUE can probably be explained by a continual immigration and/or recruitment on these fishing grounds. The fish originate from sectors that are far from towns and weakly exploited. A sociological study was carried out concurrently with the fishing survey and focused on present-day transformations within the fishing community.     

Fish stock assessment of the northern New Caledonian lagoons:1 – Structure and stocks of coral reef fish communities

Lagoon fish in New Caledonia are mainly caught by artisanal fisheries and subsistence fishing. Reef fish are the major component of this catch. The present study aimed at estimating these reef fish standing stocks and at finding the main factors influencing the distribution of these fish. Sampling of 904 stations was stratified according to three zones (north, east and west) and three reef types (barrier, intermediate and fringing). Fish communities exhibited strong heterogeneity in their distribution, showing higher biomass (maximum of 447 g·m^–2) and total standing stock (43 000 tonnes) in the north zone than in the east and west zones. Similarly, observed patterns were dependent on reef types: higher biomass and total standing stock being observed on barrier reefs than on intermediate or fringing reefs. The total standing stocks, which were about 65 000 t, were mainly composed of herbivorous fish families such as the Acanthuridae and Scaridae. The differences in the patterns of distribution of species, individuals and standing stocks between reef types may be explained by variations in terrestrial influences and reef morphology, whereas differences among zones were most likely due to accessibility of fishing areas and fishing pressure. The latter is almost non-existent in the north zone, which can thus be considered to be almost unexploited commercially. This most likely explains the high proportion, 77 %, of long-lived species in the biomass of this zone. The results might have implications in management of reefs elsewhere in the South Pacific, for which similar data are only scarcely available.     

Fishery benefits from behavioural modification of fishes in periodically harvested fisheries closures

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The bio-economic impact of mass coral mortality on the coastal reef fisheries of the Seychelles

Data collected through a stratified catch and effort survey were used to assess the impact of the 1998 mass coral bleaching event on socio-economic and biological indicators for the coastal reef fisheries of the Seychelles. There was a significant reduction in the abundance index and monthly yields per square kilometre for representatives of the family Siganidae following 1998. However, this was not associated with the bleaching event and conformed with the declining trend prior to the impact. Abundance indices and yields per square kilometre did not change significantly for the primary target families of the handline fisheries (Lutjanidae, Serranidae, Lethrinidae and Carangidae). Declining trends in abundance indices and yields for Octopodidae reversed after 1998, although the phenomena could not be independently linked to coral bleaching. Whilst critical resource based management issues are identified for the demersal handline fishery, the results suggest that there were no negative short-term bio-economic impacts on Seychelles coastal reef fisheries associated with mass coral mortality.     

三峡库区干流鱼类资源现状与物种多样性保护

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Validation of the accuracy of household reporting of subsistence fishing catch and effort: a Fijian case study

Abstract  The accuracy of household reporting of subsistence fishing catch and effort and seafood consumption on the Fijian island of Ono-i-Lau was studied. A creel survey was carried out concurrently to validate the household survey data. Reported estimates of fishing participation, effort, and fish consumption were not significantly different to the creel survey estimates. Householder's appeared to overestimate the number of fish from the most abundant family Lethrinidae, and underestimate rarer fish. However, there was no significant difference between the reported and observed contribution of the majority of finfish families and invertebrate taxa. The reported and observed catch rate estimates were not significantly different, indicating that Ono-i-Lau villagers are relatively accurate in their estimation of the number and size of fish from recalled catches.     

Composition and diversity of fish and fish catches in closures and open-access fisheries of Kenya

Abstract  Catch composition, relative abundance and diversity of fish catches in open access and three old fisheries closures were compared and contrasted with previous ecological studies. There was less variation in catch community composition among the fishing grounds than the closures, suggesting that fishing has homogenised catch composition. The trap survey found that some parrotfish [ Leptoscarus vaigiensis (Quoy &Gaimard), Calotomus carolinus (Valenciennes) and Scarus ghobban Forsskål] were relatively more common and that some important predators of macro-invertebrates [ Balistapus undulatus (Mungo Park) and Cheilinus chlorourus (Bloch)] were less common in the fishing grounds than closures. Unexpectedly, and in contrast to visual census results, cumulative number of species in catch surveys was higher in open access than closures sites. This may result from fishers covering more area and habitat or a reduction in the catch of competitively subordinate and rare species by aggressive, early-caught fish that can dominate bait. Comparisons of ecological visual census surveys and fisheries-dependent methods indicated that small differences in catch composition can reflect larger ecological differences and that baiting methods can underestimate biodiversity. Ecological impacts of fishing and large-scale changes in marine ecosystems must be considerable given the many fisheries-dependent assessments report modest changes.