Lagoon Fish Research Articles

Fishing for fortunes?A socio-economic assessment of Tonga's artisanal fisheries

Societies in the South Pacific are undergoing transition from reciprocity exchange and direct sustenance systems into cash based economies. The Kingdom of Tonga was selected to represent this socio-economic change. In this context, the economic viability of Tonga's subsistence and small-scale artisanal fisheries and marketing of reef and lagoon fish is assessed. Case studies were selected to represent three major geographical regions (Ha’apai, Vava’u, Tongatapu) and four major fisher groups (simple to very specialised and multi-geared fishing systems combined with cost of motorised boat transport, operational cost and fish market price). Marketing systems included operations of agents, middleman and shop owners. Economic assessment was performed by employing net present value (NPV) to explain the logic and to valorise fisheries and marketing systems against net revenues from employment and traditional agricultural production schemes. This paper also illustrates the limitations of conventional economic analysis. While NPV proved to be a useful instrument to compare fisheries and alternative sources of income, it failed to assess social and traditional values that determine the rather non-economical and non-rational subsistence and small-scale fisheries systems in the Tongan and South Pacific context. The conflict between applying mainly non-valorisation of societal and traditional values rather than underlying normal market behaviour rendered most fishing operations economically not viable or less attractive than agricultural production schemes and salaries from low skilled labour. Under these conditions, most Tongan fisheries do not reach the following suite of parameters required to make an operation economically attractive: minimum catch volume of 90–100 kg/week, a catch per unit effort of ≥5.8 kg/h, lowest possible operational cost and easy access to market selling prices of ≥5 TOP/kg fish. It was found that productivity increases from spear fishing to handline and multi-geared fisheries. Among small-scale fish marketing strategies, selling fish as a complementary activity to normal shop operations seems to be more lucrative than using agents and middlemen. Discussions focus on explaining the rationale of Tongan fishers by extending arguments beyond the economic and rationale framework. Major economic parameters such as labour and time are not accounted for in the traditional social environment. It is further argued that social considerations are impediments to economic rationale as they do not aim at catch maximisation, risk minimisation and innovation principles but the need to satisfy subsistence, social obligations and networking for societal resilience and insurance.

Functional groups of lagoon fish species in Languedoc Roussillon, southern France

Ten functional traits of fish species were related to habitat, diet or food acquisition, to propose a classification of 21 lagoon fishes into 10 functional groups. The selection of traits was based on their functional interest and the ease of measurement. Some groups were taxonomically related containing species belonging to the same genus, e.g. Syngnathus, Atherina or Pomatochistus. Species with a flat body shape constituted another group and three species (Anguilla anguilla, Gambusia affinis and Callionymus pusillus) formed individual groups. These results could be used to constitute functional units and to simplify such complex ecosystems and their interactions.

Local completion of the pelagic larval stage of coastal fishes in coral-reef lagoons of the Society and Tuamotu Islands

In four lagoons at two atolls and one high island in the Tuamotu and Society Islands, French Polynesia, plankton samples were taken weekly during 4 weeks in January/February 1989. A third atoll lagoon was sampled once. The lagoons varied in size and physical openness. We also sampled in the ocean near two atolls and the high island. All locations were sampled during the day, and three lagoons (two atolls and one high island) were also sampled at night. Pelagic fish eggs were more abundant in the ocean than in the lagoons at the atolls, but not at the high island. Larvae of coastal fishes were abundant in all lagoons. In the atoll lagoons, larvae of oceanic fishes were very rare to absent, but in the high-island lagoons and in the ocean, they were commonly encountered. In the ocean, larvae of many typical reef-fish taxa were abundant (58 taxa were represented by at least 10 individuals), but in the lagoons, most of these were rare or absent, and we conclude that these rare and absent taxa normally do not complete their larval phase in lagoons.

Reduction of estrogenic activity of municipal wastewater by aerated lagoon treatment facilities

The estrogenic activity of municipal wastewater in aerated lagoon treatment facilities was evaluated using plasma concentrations of vitellogenin (Vtg) in male fathead minnows (Pimephales promelas). Caged fathead minnows were exposed for 10 to 12 d in three lagoons that are connected in series at each of 10 municipal wastewater treatment facilities in central Iowa, USA, during October and November 2000. Fathead minnows held in the laboratory served as unexposed controls. Pooled (n = 4-10 fish) plasma Vtg, quantified by enzyme-linked immunosorbent assay (ELISA), was 1,702 +/- 670 (mean +/- standard error [SE]) microg/ml in the first lagoons (n = 9), 0.94 +/- 0.36 microg/ml in the second lagoons (n = 10), and 0.04 +/- 0.02 microg/ml in the third lagoons (n = 8). Differences in mean fish plasma Vtg concentration among lagoons were highly significant (p < 0.001). The mean concentration of plasma Vtg in fish in the third lagoons was not significantly different (p = 0.990) from that of the control fish (0.04 +/- 0.02 microg/ml). Plasma Vtg concentrations of fish in the first lagoons were inversely correlated with wastewater retention time in the lagoons (p = 0.002, r = -0.877). Water temperatures of the final effluents during the study ranged from 9 to 12 degrees C. General treatment efficiency of lagoons has been shown to be dependent on temperature, so the potential exists for decreased removal of estrogenic activity when water temperatures are lower (e.g., winter months) than the present study. In conclusion, wastewater entering aerated lagoon systems was estrogenic to fish, but with serial passage through the lagoons, the estrogenic activity decreased to a level that was not sufficient to induce vitellogenesis in male fathead minnows in a 10- to 12-d exposure.

Impact of fishing on fish assemblages in tropical lagoons: the example of the Ebrie lagoon, West Africa

Lagoon fish communities often consist of complex assemblages of numerous species, difficult to manage with conventional stock assessment models. Useful data are still lacking for evaluating the importance of man-made disturbance and reference situations are missing, especially in developing countries. As a consequence, by analysing data collected 20 years ago in two of the six sectors of the Ebrie lagoon (Ivory Coast), this study aims to evaluate the impact of fishing effort on fish assemblages. These two sectors (V and VI), located far from the inlet, have similar physical, chemical, biological and fish fauna characteristics. The major difference lies in the fishing intensity: sector VI has a low fishing intensity (fishing for personal consumption using only individual gear), whereas sector V is heavily fished (professional fishing with both individual and collective gear, particularly beach seines which result in a considerably higher fishing effort). Comparisons between the two sectors were based on two complementary scientific approaches: a 3-year commercial fisheries survey (1978-1980) and a 1-year experimental survey (1981). The impact of fishing on fish assemblages is analysed through the main characteristics of fish populations and communities. The results show that there were major changes including an increased catch yield (37.5-189 kg ha –1 y –1), a lowering of fish diversity in catches, of fish biomass (100-20 kg ha –1), of average catch length (22.6-14.6 cm) and of trophic level of catches (26-58.5% of herbivore/detritivore species in total catches). Such results are quite unusual because they occurred even in non-overfished ecosystems: the fish assemblage was deeply modified in sector V compared to the lightly fished adjacent sector VI, even though fishing effort in sector V was only high but at a reasonable level. These data must be completed by similar studies in tropical lagoons with variable levels of fishing intensity in order to understand fish assemblage re-organization when submitted to stresses of different intensity.

Factors Influencing Fish Composition in an Australian Intermittently Open Estuary. Is Stability Salinity-Dependent?

The ichthyofauna of the intermittently open Shellharbour Lagoon in southeastern Australia was sampled over 14 months to investigate factors influencing species composition. Zostera capricorni and bare sand habitats were sampled every two months with a fine-mesh seine. Of the 10277 fish caught representing 19 families and 27 species, the most numerically dominant species were Pseudogobius olorum and Pseudomugil signifer. The most abundant economically important species were Acanthopagrus australis, Mugil cephalus and Myxus elongatus. Mean number of fish and species was significantly higher over Zostera than bare sand during months immediately after the estuary opened when juvenile marine fishes recruited, demonstrating the estuary's nursery function. In contrast to other intermittently open estuaries in Australia and South Africa, Shellharbour Lagoon's fish assemblage appears resilient to perturbation and does not undergo distinct seasonal variations. This may be a result of the estuary's short open phases providing less opportunity for marine fishes to enter. Perhaps more importantly, the less dramatic fluctuations in salinity between open and closed phases maintains salinity at a level intermediate of the tolerances of both marine and estuarine fishes.

Effects of El Niño-related Drought on Freshwater and Brackish-water Fishes in Suriname, South America

Droughts associated with the El Nino-Southern Oscillation (ENSO) affected fishes of brackish-water lagoons, freshwater swamps and a rainforest creek in Suriname, South America. The mean rainfall in the period August to February in 22 El Nino years was 76.6% of the mean rainfall in the same months of non-El Nino years. In the period 1900–1999, three out of four years in which an extreme drought (rainfall less then 60% of the mean value) occurred were El Nino years. The recent 1997/1998 ENSO event caused the second most severe drought in a 100-year record. Drying up of brackish-water lagoons, freshwater swamps and rainforest creeks was observed during El Nino-related droughts. In the lagoons ariid catfish died first, followed by snook, tilapia, mullet and tarpon, respectively. Landings of lagoon fish were positively correlated with rainfall in the period August–February. During the El Nino-related drought we observed failure of reproduction in three species of callichthyid armoured catfish in both coastal freshwater swamps and a rainforest creek in the interior. In the El Nino year 1997/1998, the ‘no flow’ period of the rainforest creek was extended by four months beyond the long dry season and the dissolved oxygen levels in the dry-season pools dropped to 1.27 mg O2l−1 (as compared to 4.53 mg O2 l−1 under running water conditions). Other fish species of the rainforest creek also showed decreased reproductive success in the El Nino year. We suggest that the stochastic effects of El Nino-related drought may be an important non-equilibrium component in the ecology of neotropical inland fish communities.

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.

Empirical evidence of a trade–off between reproductive effort and expectation of future reproduction in female three-spined sticklebacks

Optimal life-history models generally predict that the reproductive effort of iteroparous organisms may increase with age, as their expectation of future reproduction decreases. The population of three–spined sticklebacks ( Gasterosteus aculeatus ) in the Camargue (Rhone River Delta, France) is annual, all adults dying after their first breeding season. As the three–spined stickleback is a multiple spawner, we tested the hypothesis that reproductive effort may increase during the breeding season on field data. From 1987 to 1998, 653 female sticklebacks were collected in the field during the breeding seasons. The body size, body weight and weights of the liver, gonads and carcass were measured for these individuals. Only gravid females with mature eggs (176 fish) were included in the analysis. Considering the female three–spined stickleback as a capital breeder, the energetic resources available for allocation between soma and gonads were estimated by its body weight. Somatic condition decreased during the breeding season and reproductive effort (gonad weight relative to body weight) increased. These patterns did not vary significantly between years. These observed variations in reproductive effort during the breeding season can be interpreted as empirical evidence of a trade–off between reproductive effort and expectation of future reproduction.

Kenyan coral reef lagoon fish: effects of fishing, substrate complexity, and sea urchins

Population density, number of species, diversity, and species-area relationships of fish species in eight common coral reef-associated families were studied in three marine parks receiving total protection from fishing, four sites with unregulated fishing, and one reef which recently received protection from fishing (referred to as a transition reef). Data on coral cover, reef topographic complexity, and sea urchin abundance were collected and correlated with fish abundance and species richness. The most striking result of this survey is a consistent and large reduction in the population density and species richness of 5 families (surgeonfish, triggerfish, butterflyfish, angelfish, and parrotfish). Poor recovery of parrotfish in the transition reef, relative to other fish families, is interpreted as evidence for competitive exclusion of parrotfish by sea urchins. Reef substrate complexity is significantly associated with fish abundance and diversity, but data suggest different responses for protected versus fished reefs, protected reefs having higher species richness and numbers of individuals than unprotected reefs for the same reef complexity. Sea urchin abundance is negatively associated with numbers of fish and fish species but the interrelationship between sea urchins, substrate complexity, coral cover, and management make it difficult to attribute a set percent of variance to each factor-although fishing versus no fishing appears to be the strongest variable in predicting numbers of individuals and species of fish, and their community similarity. Localized species extirpation is evident for many species on fished reefs (for the sampled area of 1.0 ha). Fifty-two of 110 species found on protected reefs were not found on unprotected reefs.

Heavy metals and organisms in the Lagos Lagoon

Levels of cadmium, cobalt, copper, chromium, iron, manganese, nickel, lead and zinc were determined in the water and in some fish and shellfish in the Lagos Lagoon. The levels in the water were 3–5 orders of magnitude lower than the values reported for the sediments. They were also very much below the maximum allowable levels in marine waters set by the United States Environmental Protection Agency (US. EPA). The implication is that waste assimilation capacity of the system is high, a phenomenon attributable to dilution, continuous water exchange and sedimentation. Except for lead levels in fish, the metals were at low levels in the organisms. However, when compared with levels determined in fish from a rural river, relative enrichment in the lagoon fish, ranging from about 2 for lead to 66 for copper was observed, implying that urban and industrial wastes discharged into the Lagos Lagoon have had a significant impact on the ecosystem. High‐petrol lead is believed to make a substantial contribution toward...

Distribuição e ciclo de vida das espécies de peixes mais abundantes da laguna de Marapendi, Rio de Janeiro, Brasil

Monthly sampling from march 1981 to april 1983 using beach seines, cast nets and gill nets indicated six species, Xenomelaniris brasiliensis, Brevoortia pectinata, Geophagus brasiliensis, Gerres aprion, Genidens genidens and Achirus lineatus, as the most abundant fishes in the Marependi Lagoon, Rio de Janeiro, BraziL The species presented a long reproductive period and the recruitment distributed throughout the year. Analysis of the mean catch per unit effort in relation to month, sampling areas, and environmental factors along with analysis of the length frequency distribution by depth strata indicated that the spatial distribution, related to depth and occurrence of submerged aquatic vegetation seem to be the main factors regulating the species distribution. Alteration of the environmental conditions in the lagoon due to the opening of the Marapendi channel in 1984 caused significative modification in the distribution and abundance patterns of the main species. The impact of these alterations in the Marapendi Lagoon fish community has yet to be determined.

Diets of lagoon fishes of the Solomon Islands: Predators of tuna baitfish and trophic effects of baitfishing on the subsistence fishery

Analyses of the stomach contents of 122 species of predators from fringing reef lagoons of the Solomon Islands showed that 45 species ate baitfish species caught commercially. Baitfish (mainly Stolephorus and Spratelloides species) comprised nearly 25% by weight of their combined diets, but in only 28 of these predators were baitfish a major proportion of the diet. To simulate the subsistence fishery, fishing competitions (using drop-lining, spear-fishingand trolling) were held. A total of 183 species of 31 families was recorded. Drop-lining, the predominant technique, contributed most to the overall catch, although trolling was important in one area. Catches from traditional poisoning methods were also monitored. We concluded that most of the fish caught by the subsistence fishery do not eat baitfish. Some pelagic species, mainly Scombridae, are baitfish predators, but are caught only by trolling. Hence, unless there is a marked increase in trolling among subsistence fishermen, there is little evidence that the commercial baitfishery at present directly affects the food chain on which the subsistence reef fishery depends.

Distribution of Mercury in the Sediments and Fishes of the Lagoon of Aveiro, Portugal

Dry and wet sieving were compared on their suitability for the size fractionation of bottom sediment samples, collected from a brackish water, coastal lagoon, prior to flameless atomic absorption analysis of the sediment concentration of total mercury. The work aimed at identifying the most important point sources of mercury to the lagoon waters and at assessing the distribution, throughout the ecosystem, of the mercury discharged. The results reported in this paper refer to the lagoon sediments and fishes. Ongoing work is extending the survey to the other inland ecological niches and to the coastal waters and sediments. A chlor-alkali plant proved to be the most important source of mercury but its contribution has not yet been disentangled from those originating at a pyrite roasting facility and a PVC factory operating in the same industrial park. Sewage discharges from the bankside communities are the other significant point sources of Hg. Concentrations of Hg in the superficial sediments ranged from 850 mgkg−1, near the chlor-alkali sewer outlet, to 0.05 mgkg−1 in the intertidal sands of the coastal beaches. Sewage-affected sediments have concentrations of Hg in the range of 1 to 2 mgkg−1. The concentrations observed in the water samples and superficial sediments suggest that some of the Hg historically discharged into the lagoon may have been exported to the Atlantic Ocean coastal waters. Bioaccumulation of Hg in fish tissues shows the usual dependence on species, territoriality, feeding habits and size. Concentrations as high as 25 mgkg−1 fresh weight have been observed but the average values do not exceed the EEC quality objective of 0.3 mgkg−1 (EEC, 1982).

MODES OF TRANSMISSION OF CHOLERA IN A NEWLY INFECTED POPULATION ON AN ATOLL: IMPLICATIONS FOR CONTROL MEASURES

To determine the modes of transmission in a cholera epidemic in a newly infected population on an atoll, two studies were conducted, in which persons with cholera were individually matched, by age and sex, with neighbourhood controls. Among the first recognised cases, cholera was associated with frequent (daily or weekly) consumption of raw lagoon fish that had been salted and partially dried. Vibrio cholerœ was isolated from the lagoon, which was contaminated by human wastes. During the declining phase of the epidemic, cholera was associated with consumption of raw clams, salt-fish, sardines, and other fish from the lagoon. When seafood from enclosed bodies of fæcally contaminated water is frequently eaten raw, imported V. cholerœ can become established and can be extremely difficult to eradicate.

Balof Shelter, New Ireland—report on a small excavation

The excavation of 6 [sq m] from a rock shelter in New Ireland is described. The maximum depth of deposit was 80 cm, with no clear strata being visible. A radiocarbon date of 6–7,000 years b.p. was obtained from the lowest levels, and one of 2,500 years b.p. from the middle. Faunal materials recovered include mammals (all except one still extant), lagoon fishes, reptiles and shellfish, the last being primarily from reef and lagoon environments. Artefacts from earlier levels include bone bi-points, flaked stone tools patterned similarly to those from the New Guinea Highlands and made from stone from a variety of resources, and obsidian imported from Talasea, New Britain. Obsidian from the Lou (Admiralty Is.) source, and pottery date from about 2,500 years ago. The site is the oldest so far excavated in Melanesia, and data from it provide insights into the development of trade patterns in the area over the last 7,000 years.

Ultrastructure of the cell types and of the neurosecretory innervation in the pituitary of Mugil cephalus L. from freshwater, the sea, and a hypersaline lagoon : III. The neuro-intermediate lobe

The neuro-intermediate lobe of the pituitary was studied in specimens of Mugil cephalus taken from biotopes of varying salinities. The neurohypophysis in hypersaline lagoon fish was larger than in those caught in freshwater or the sea. The distal neurohypophysis of lagoon adapted specimens was characterized by a large number of “pale” neurosecretory granules, an increase of microtubules in the subterminal region of the axons and an abundance of fibrillar pituicytes. These signs could indicate that the neurohypophysis has a specific role in the adaptation of M. cephalus to high salinities. Pars intermedia tissue consisted of periodic acid-Schiff staining cells on the “islet” borders and of melanophore expending hormone (MSH) cells inside the “islets.” The endoplasmic reticulum of the MSH cells was hypertrophied in freshwater specimens. Pars intermedia tissue contained neurosecretory axons of both the A- and B-types; A-type axons were particularly profuse, some of them making synaptoid contact with MSH cells.

First Experiments on the Rearing of Tropical Carangidae in Floating Cages

ABSTRACTIn order to determine the feasibility of fish culture in French Polynesia's lagoons, preliminary tests were performed in 1973 and 1974. Juveniles (7 to 10 g) of three Carangidae species (Caranx melampygus, C. elacate, C. ignobilis) were caught in the wild and transported to the laboratory; three lots were dispatched among two small tanks (500 liters) with 10 animals each and a floating cage (6 times 6 × 4 m; 1.5 cm mesh) with 900 animals.The range of water temperature was 25 to 27 C, salinity was about 34.5 ppt, and pH was 8.2. Food was given in the form of a moist pellet consisting of 80% dry powder mixed with fresh bonito flesh or troca flesh. Such a diet has a 40% protein content due essentially to fish meal (sun‐dried lagoon fish). These moist pellets were well accepted, but dry pellets were spat out.The time necessary to get a commercial size (300 g) in the tanks or in the floating cage was 6 to 8 months. Mortality rate was under 5%. The net of the floating cage was kept clean by a herbivorous fish (Siganus sp.) associated with Jack‐fish.Jack‐fish culture in lagoons seems promising because of its desirable meat, high market value, and rapid growth rate. Studies are being carried out to demonstrate the economic feasibility of such a culture by reducing the cost of feed and by obtaining reproduction in captivity.

The Use of Rotenone for Collecting Reef and Lagoon Fishes at Bikini

The Use of Rotenone for Collecting Reef and Lagoon Fishes at Bikini