The experiments described in this paper relate known target configurations under controlled conditions to acoustic characteristics of multiple moving fish. We wanted to further our understanding of the interactions between targets and the effects these interactions have on the measurement of the number of salmon migrating in rivers. Multiple targets in various configurations were passed through a horizontally oriented 4° × 10° beam from a split-beam echo sounder. The effects on measurements of target strength, detection probability and target location in the beam are presented. The observed target strength was not dependent on target velocity. There was a reduction in target detection due to the single-target selection criteria implemented by the hydroacoustic system. We mimicked the conditions in a river where a close range fish target may modify the beam geometry allowing detection of previously undetected targets. We demonstrated some of the effects resulting from moving targets into radial alignment and we demonstrated shadowing conditions that can cause extinction of target echoes.

Daily growth increments measured in the otolith of Thunnus atlanticus were used to estimate the age and growth of individuals, which were sampled from an artisanal fishery operating around fish aggregating devices (FADs) moored off Martinique Island. In this study, 76 otoliths were analysed for fish ranging from 20 to 68 cm fork lengths (FL). The fish were caught using trolling lines at depths ranging from 0 to 10 m. Counts were made, under a light microscope, on the external part of the transverse section of the sagittae, from the primordium to the ventral edge. The mean coefficient of variation of the age reading was 2.4%. To validate readings, the number of increments for 11 individuals was counted using both optic and scanning electron microscopes. The calculated relationship between readings of both methods was found to be linear, with a slope of 1.03 and R2 = 0.99. Frequency of growth increment formation could not be validated. Growth rates derived from otolith readings were, however, compared to those obtained using a modal progression analysis, which was performed on the length-frequency distributions of the landings over a period of two months. The corroboration between the growth rates was good. One increment was assumed to represent one day. The parameters of the von Bertalanffy growth curve for both sexes were L∞ = 71.4 cm FL, k = 0.002 day−1 and t0 = −80 days. According to our results, there is no evidence that Martinican moored FADs act as ecological traps for blackfin tuna. Instead, young blackfin tuna probably leave the vicinity of Martinican moored FADs to undergo a trophic migration at 7 to 8 month-old, and then come back about 8 months later to breed in the Lesser Antilles area.

Bivalve molluscs are filter feeders and as a consequence they may bioaccumulate in their tissues viruses that infect humans and higher vertebrates. However, there have also been described mortalities of bivalve molluscs associated with viruses belonging to different families. Mass mortalities of adult Portuguese oysters, Crassostrea angulata, among French livestocks (between 1967 and 1973) were associated with irido-like virus infections. Herpesviruses were reported in the eastern oyster, Pacific oyster and European flat oyster and lately in scallops and clams. Disseminated neoplasia, a proliferative cell disorder of the circulatory system of bivalves, although of uncertain aetiology, has been suggested to be caused by retroviral infections. Other viruses described in bivalves are interpreted as members of the Papovaviridae, Togaviridae, Reoviridae, Birnaviridae and Picornaviridae. However, the lack of bivalve cell lines renders difficult virus isolation from molluscs although some viruses can be isolated in fish cell lines.

A comparative study, using biological indicators, was conducted in Mali where two man-made reservoirs (Selengue and Manantali) are particularly suited for investigating the impact of fishing effort on the fish assemblage: these two ecosystems have relatively similar morphological, edaphic and environmental properties but are subjected to radically different levels of fishing exploitation (low at Manantali, high at Selengue). The comparison is based on a three-month survey of commercial fisheries, focusing on fishing activities and catches on the two reservoirs.

The results show that some indicators are useful for evaluating fishing impacts. Among these indicators are: fishing effort which is much higher at Selengue (22 800 fishing trips per month) than at Manantali (3000), catches per unit effort (lower at Selengue than at Manantali following a ratio ranging from 1.5 to 4 according to the gears used), annual yields per ha higher at Selengue (100 kg ha−1) than at Manantali (27 kg ha−1), the average fish lengths in the catches (16.2 cm at Selengue compared to 23.6 cm at Manantali) and the maximum lengths of the targeted species generally smaller at Selengue (10 to 30 cm) than at Manantali (30 to 50 cm). By contrast, a second class of indicators exhibit values that are contrary to expectations: the species richness (52 compared to 36), the species diversity (Ish = 4.02 compared to 3.24) and evenness (0.76 compared to 0.69) were higher at Selengue where 4 species accounted for 50% of the landings compared to only 2 species at Manantali (9 species compared to 7 for 80% of the landings). The trophic structure of the landings is higher (37% primary consumers compared to 49% at Manantali) as well as the mean trophic level (2.74 compared to 2.54 at Manantali).

Even if a good understanding of the two fisheries can explain the unexpected trends of the second class of indicators which increase with fishing effort, it clearly appears from this study that only the first class of indicators is robust and can be used for comparative studies across ecosystems.

The genus Perkinsus includes protistan parasites infecting marine molluscs throughout the world, some of which are associated with mass mortalities. Life cycle involves vegetative proliferation within the host, by which a cell named trophozoite undergoes successive bipartitioning. Other stages have been observed in vitro or in vivo, depending on the species: hypnospore, zoosporangium and zoospore. Molecular taxonomy supports a close affinity between dinoflagellates and Perkinsus spp. Six species of Perkinsus are currently considered valid: P. marinus, P. olseni, P. qugwadi, P. chesapeaki, P. andrewsi and P. mediterraneus. Histology and, above all, incubation of host tissues in Ray's fluid thioglycollate medium (RFTM) are classic diagnostic methods. In addition, more sensitive and quicker molecular diagnostic techniques based on either immunoassays or PCR have been developed for Perkinsus spp. Epizootiological studies have shown a marked influence of water temperature and salinity on P. marinus infection in oysters Crassostrea virginica, thus determining parasite geographical range and temporal disease dynamics (seasonality). In vitro cultures have been established for four Perkinsus spp. Immune response to infection varies depending on host and involves phagocytosis or encapsulation of the parasite cells by host haemocytes. A polypeptide is secreted by clam Tapes philippinarum haemocytes that could kill the parasite. In vitro cultured P. marinus cells secrete proteases that are likely involved in degradation of host tissues. P. marinus can suppress the toxic oxygen radicals produced by host haemocytes. In addition to host death, sublethal effects caused by Perkinsus spp. (reduction of fecundity, growth, and condition) may have significant ecological and economic implications. Various strategies have been assayed to mitigate the consequences of P. marinus epizootics on the oyster industry: modifications of management/culture procedures, selective breeding to obtain resistant oyster strains, and the use of triploid oysters and allochthonous oyster species. Some chemotherapeutants have been proved to inhibit or kill parasite cells in vitro.

The effects of nitrite (NO2–) on the Nile tilapia (Oreochromis niloticus) were investigated, due to their relevance to worldwide aquaculture. Hematological parameters – functional haemoglobin (oxy+deoxy-Hb, %), methaemoglobin (MetHb%), and hematocrit (Hct) – and – plasma osmolality, plasma chloride ([Cl−]) and magnesium ([Mg2+]) concentrations – were analysed. Two experiments were conducted, each with its own non-contaminated control, 8 tilapias for each group. In experiment 1 (48 hours), and the first 48 hours of experiment 2, fish were contaminated with 0.4 mM NO2– (added as NaNO2). In experiment 2, ambient NaNO2– was removed for the second 48 hours. NaNO2– exposure increased plasma [NO2–] to 0.4 mM, which increased MetHb from 10.8 ± 2.5% to 46.8 ± 8.0%, and consequently decreased functional Hb from 89.2 ± 2.5% to 53.2 ± 8.0%. NaNO2 removal led to recovery of both parameters. Both Hct and plasma Mg2+ were lowest in fish recovering from nitrite exposure. Thus, these parameters did not show recovery. Plasma osmolality and [Cl−] were not affected by NaNO2–, probably due to the moderate rise in plasma [NO2–]. O. niloticus was thus sensitive to 48 hours of exposure to 0.4 mM NaNO2, and partially recovered from its effects after 48 hours in sodium nitrite-free water. Cultivators of Nile tilapia should thus consider the toxicity of nitrite, especially in aquaculture systems using recirculating water.

Among mollusc pathogens, paramyxeans are an important group of protistan parasites belonging to the genera Marteilia and Marteilioides. Marteilia refringens and M. sydneyi are of particular concern given their potential impact on mollusc aquaculture world-wide. Aber disease and QX disease are currently listed by the OIE, the World Organisation for Animal Health. After more than thirty years of existence in the scientific literature, these organisms still pose questions and research challenges to investigators. This paper reviews current knowledge of the group and key references. The review was focused on taxonomy, epidemiology, pathology and potential control methods for these organisms in order to enhance understanding of paramyxean infection issues in mollusc aquaculture.

An investigation was carried out into the PAH chemical contamination resulting from the “Erika” tanker fuel spillage of December 1999 along the French coast of the Bay of Biscay. A qualitative and quantitative assessment was conducted of this contamination in water, suspended particulate matter, sediments, and in intertidal molluscs. The chemical composition of PAHs in pre-spill and post-spill samples was determined and used to distinguish the “Erika's” fuel as the source of PAHs in the coastal environment of the Bay of Biscay. Changes in concentrations of PAHs were also assessed. The GC-MS analysis made it possible to identify and quantify parent unsubstituted PAHs, alkyl-substituted PAHs (C-PAH) and sulfur heterocycle unsubstituted and alkyl substituted compounds (SPAH and C-SPAH). The results of this study demonstrated that heavily oil-contaminated shorelines, including beaches, rocky coasts as well as sandy sediments apparently became reservoirs of spilled fuel and these continued to contaminate seawater, suspended particulate matter and mussels with PAHs. These conclusions were borne out by the following observations: (1) the pattern changes in PAH composition after the “Erika” oil spill were consistent in all contaminated compartments (water, suspended particulate matter SPM, intertidal sediments and molluscs), (2) the compositional patterns of PAHs after the “Erika” oil spill in contaminated water, SPM, intertidal sediments and molluscs constantly included alkyl-substituted phenanthrenes, pyrenes, chrysenes and sulfur heterocycle compounds in higher relative abundances than those in the pre-spill samples of these compartments, (3) the relative abundances of different suites of PAHs at contaminated sites were similar to those of weathered “Erika” fuel, (4) consistent and visible temporal decline in concentrations for water, SPM and molluscs, (5) the geographical contiguity of the stations with high concentrations of PAHs in molluscs matched the extent of the shoreline contamination by the spilled fuel. The increase in the contamination levels before and after the spill, together with the significant change in the pattern of PAH composition provide evidence of the intense and long-term chemical contamination of the “Erika's” fuel and of the damage to natural marine resources resulting from such contamination by toxic oil components.

Seasonal changes in nucleic acid concentrations and amino acid profiles in the muscle of juvenile Aristeus antennatus were investigated. RNA content, RNA:DNA and RNA:protein ratios varied significantly between seasons (p < 0.05), being the lowest and the highest values obtained in winter and spring/summer. A significant variation in the total amino acid content (TAA) from winter to summer was observed (p < 0.05). In fact, during this period a significant percent of increase in total non- (NEAA; 20.2%) and essential amino acids (EAA, 18.7%) contents occurred. Concomitantly, a significant decrease in the free amino acid (FAA) content from winter to summer was observed. A higher percentage of decrease with free essential amino acids (FEAA; 56.6%) in comparison to free non-essential amino acids (FNEAA; 34.2%) was attained. The significant increase in RNA and TAA contents from winter to summer may be related with protein synthesis. On the other hand, the lowest values obtained in winter may be due to a reduction in feeding activity; in this period the muscle protein must be progressively hydrolysed, which is evident with the higher FAA content. The liberated amino acids enter FAA pool and become available for energy production.

A parameter of a model becomes a decision support indicator if it is used as an argument of a decision function. This implies consideration of a wider model than the initial one and to acknowledge its complexity. It is also necessary to include the estimation of parameters in indication theory and to consider a data driven approach. Data analysis leads us to provide sets of indicators. With reference to the statistical concept of sufficiency (Fisher 1925), such a set may also be considered as a set for indication, equivalent to the original data for any subsequent purpose of indication. From the same data set, several models may be built providing different sets for indication. None of them can be considered as the best; this depends both on the context (e.g. fishing practices) and on the addressed questions. No model must be chosen to the exclusion of alternatives: an illustration is given with models in relation to a catch-effort data set, with a case study on Senegalese small scale fisheries.

Since March 2001, samples of the remaining oil from the wreck of the “Erika” have been collected along the Atlantic coastline in order to assess the natural degradation rate. Four years after the sinking of the tanker, chemical analyses of the oil revealed the influence of environmental parameters on the degradation kinetics. Among the diverse parameters controlling the fate of oil in the environment, biodegradation by microorganisms is known to play an important role. To investigate the role of microorganisms on “Erika” oil degradation, microbial mats from the Guérande salt marches were maintained in slurries containing the pollutant. From these slurries experiments, a low biodegradation rate of the “Erika” oil was detected indicating the degradation capacities of microbial mats. Biodiversity studies were conducted to further understand the biodegradation processes. Microbial mats from the Guérande salterns were maintained in microcosms to evaluate the impact of “Erika” oil on bacterial communities. Molecular analysis based on 16S rRNA and pufM encoding genes allowed fingerprinting of the bacterial and purple anoxygenic bacterial (PAB) communities respectively. These studies revealed bacterial diversity and communities changes showing the adaptation of microorganisms to the “Erika”.

The first internal transcribed spacer (ITS-1) of nuclear ribosomal DNA and mitochondrial DNA 16S rRNA were amplified by Polymerase chain reaction (PCR) using genomic DNA extracted from adult tissue of four species of Scylla spp. and the first zoeal stages of S. serrata, S. paramamosain and S. olivacea as template. Using the ITS-1 region, variation in product fragment length was found to be useful for distinguishing S. serrata and S. olivacea from two other species. The other two species (S. paramamosain and S. tranquebarica) could be identified using the restriction endonuclease Hha I. Using 16S rDNA, all four species were identified using PCR-restriction fragment length polymorphism (RFLP) by double digestion with DraI and HindIII. These genetic markers can be used for hybridization breeding studies and in field studies of larval and juvenile mud crabs of the genus Scylla.

This review summarizes the current state of knowledge regarding the two primary proliferative diseases of commercially important marine bivalves. Disseminated neoplasia is characterized by the presence of large (2−4 times the diameter of normal hemocytes), anaplastic, circulating cells that have a hyperchromatic and often pleomorphic nucleus containing one or more prominent nucleoli. Prevalence exceeding 90% has been reported; the disease is progressive and can result in significant mortality of affected populations. Softshell clams, Mya arenaria, and mussels, Mytilus trossulus, from the east and west coasts of North America, respectively, and cockles, Cerastoderma edule, from Ireland, appear to be especially susceptible. Disseminated neoplasia can be transmitted to uninfected individuals, indicating an infectious (perhaps viral) etiology, the expression of which may be aggravated by environmental degradation. Gonadal neoplasia consists of small, basophilic, undifferentiated cells that originate as small foci in gonadal follicles where they proliferate and eventually invade surrounding tissues. This disease primarily affects M. arenaria in Maine (USA) and Mercenaria spp. in Florida (USA) at prevalences up to 50%. Most affected individuals are female. Limited field studies to date indicate that the disease progresses slowly and mortality rates are low. The major impact is most likely a reduction in reproductive effort. The finding that prevalence of gonadal neoplasia is higher in hybrid Mercenaria spp. suggests a genetic etiology. Precise determination of the etiology and other aspects of both diseases will benefit greatly from future advances in cellular and molecular biological techniques.

Fishing pressure on reef fish stocks, in relation to exploitable biomass, is a useful parameter for fishery resource management but difficult to assess in subsistence fisheries. A methodology for indirect fishery output assessment in island environments is proposed based on estimates of consumption and the relevant seafood trade. Ouvea atoll in the South Pacific (Loyalty Islands, New Caledonia), where subsistence fishing is the main activity, was used as the experimental site. A consumer survey of the islands' households was conducted in June 2000. The sampling plan was determined on the basis of data already available on the population concerned, making it possible to give quantitative and qualitative information on catches. Total catch is estimated to be 212 t y−1 composed mainly of Lethrinidae, Serranidae and Gerreidae. Subsistence activity is the main source of supply for two-thirds of households. These results were validated by a survey carried out on fishers at the same time that confirms the reliability of fish consumption as an indicator of reef fish catches. This study also showed that shoreline fishing remains the main activity in Ouvea: it's practised by 71% of households and provides almost 48% of total landings. A second stage was the identification of variables liable to influence consumption patterns: fishing practice (frequency and gear type), income, and household size seemed to be the main determining factors. These variables were integrated into a multi-dimensional analysis in order to define types of consumers. This consumption-based approach underlies a sampling strategy that could be extrapolated to other small South Pacific islands. It involves advantages of various kinds – accuracy, reliability, and cost-effective implementation – that make it a powerful tool for monitoring island fishery development.