A simulator dedicated to the modeling of individual search behaviors of fishing vessels has been built using multi-agents systems methodology. The harvesting activity of a virtual fleet is simulated and applied to a static virtual fish population, distributed in a bi-dimensional spatially explicit environment. The resource population can differ depending on different degrees of aggregation. Each vessel of the fleet is modeled as a singular and autonomous agent of the fishery system. The model focuses on the representation of information transfer among vessels, which results in an orientation of search effort. The informative search behavior is compared to a stochastic search, in order to estimate efficiency gains allowed by information transfers. Results show a strong dependence of the fleet's efficiency towards the level of aggregation of the resource. For higher levels of aggregation the informative behavior results in important gains in efficiency. Conversely, a misleading effect of information appears in the weakest aggregations. The informative behavior leads to the progressive convergence and the gathering of the agents. When the aggregation is strong, this “pack effect” is stable in time and enables the vessels to make quick catches. For the weakest aggregation levels, the “pack effect” is unstable and leads the ships to a perpetual pursuit state, without catches. Thus, the size of existing networks appears as a key parameter of vessel behaviors. This approach, using an individual-based simulator, seems quite appropriate to connect individual behaviors to the dynamics of the fishing efficiency, which are generally studied in an aggregated manner. It allows to quantify the effects of the exchange of information among vessels, which is commonly considered as a qualitative phenomenon. Such an approach should be enlarged to a more global modeling of all of the components of the individual search behaviors of vessels.

In this paper, we present an approach to compare the impact of different management options on the dynamics of a mixed fishery. We used ISIS-Fish, a simulation tool aimed at evaluating the impact of spatial and seasonal management measures on the dynamics of mixed fisheries. The French Nephrops norvegicus (Norway lobster) – Merluccius merluccius (hake) mixed fishery of the Bay of Biscay was chosen as a study case. First, we parameterised the population and exploitation models. We then selected several management measures, including marine protected areas (MPAs) and total allowable catches (TAC), and parameterised fishermen's reaction to each measure. Then, a sensitivity analysis was performed according to a fractional factorial experimental design. Management scenarios were assessed and compared using a statistical simulation design. The sensitivity analysis showed the large influence of some parameters, such as natural mortality, N. norvegicus fecundity, and catchability on both abundance and catches. Given model parameters, an improvement of trawl selectivity and several MPA designs (differing in size, seasonality and location) were found to result in a significant increase in abundance over 10 years, especially for N. norvegicus. This study illustrates the need for a pluri-specific approach to fisheries assessment and management.

Growing pressures from development activities, on aquatic environments in South American countries, have created an urgent need for tools to measure the quality of aquatic systems. The index of biotic integrity, based on fish assemblages, elaborated in North America, constitutes a basis for the development of these tools. However, its direct application is problematic in regions having a rich and diverse ichthyofauna and where the knowledge of fish species ecology is incomplete. The response of taxonomic or trophic groups is often unknown and the selection of fish assemblage metrics cannot be based on previous knowledge, as in intensely studied regions. This work proposes a method, similar to the approach recently pursued in Europe, based on comparing the variability of fish assemblages in reference situations with their variability influenced by human-induced perturbations. The method was developed from 53 samples of 27 reaches in 7 hydrographic basins of French Guiana. For each of 28 fish assemblage descriptors, stepwise multiple linear regressions with 28 habitat variables were carried out. The residuals of the models obtained were used as candidate metrics independent of natural environmental factors. Nine metrics showing significant differences between reference and disturbed samples were selected to constitute the index. The index was validated by analysing a temporal data series obtained from a reach disturbed by dam construction.

The objective is to study different factors of variations in the body shape of trout (Salmo trutta) belonging to the Mediterranean lineage (indigenous trout) or Atlantic lineage (introduced trout), and their hybrids. Using thin plate-spline (TPS) method by pointing landmarks, it made possible to provide a graphical representation of the characteristic conformation of the individuals. The characteristics of form highlighted let appear – that the male trout have a dorsal part more prominent than that of the female trout and a larger head – the existence of a general curvature of the body related to the size of trout, independently of the sex. In addition, characteristics of form provide satisfactory results to distinguish the Mediterranean lineage from the Atlantic lineage. The recognition of hybrid trout is more random because very near to Mediterranean trout. The existence of a sexual dimorphism could be established in spite of the absence of information on the sex. Comparative with the sexual dimorphisms in spawning period reveals morphological transformations during the reproduction, mainly for the males. Independently of the genotypic and sexual dimorphisms, a general curvature of the body related to the size was detected.

Neosalanx reganius is a poorly studied salangid fish restricted to the upper reaches of the Chikugo and the Midori River flowing into the Ariake Bay, Kyushu, Japan. Samples of N. reganius were collected from brackish water areas of the Chikugo River by eight cruises in 1998-2004 to characterize the distribution pattern, feeding ecology in relation to ambient prey concentrations, fecundity and condition of the fish. A total of 244 specimens were collected, 36 to 71 mm total length, and 111 to 1301 mg body weight. The catch per unit of effort (CPUE; number of fish collected by towing a larva net for 20 min) correlated positively with turbidity and negatively with salinity. N. reganius is a planktivorous fish, fed on a single calanoid copepod species Sinocalanus sinensis, which was the single most dominant prey item in all stations during all cruises, contributing as high as 97.0% of the total diet of the fish; the other prey items (other calanoids and cyclopoids, Daphnia sp. and decapod mysid) together contributed only 3%. S. sinensis also dominated in the environmental copepod composition. The CPUE showed significant correlation with copepod dry biomass which increased upstream (r = 0.90; p < 0.05). Fecundity ranged 347-995 (mean 583 173) oocytes individual−1 and relative fecundities ranged 6.8-15.6 (mean 10.1 ± 2.4) oocytes mm−1 TL and 0.8-2.5 (mean 1.6 ± 0.5) oocytes mg−1 of net body weight (weight taken after gonad extraction). Fecundity showed significant positive relationship with fish length and body weight. GSI ranged 29.4-58.8% (mean 43.5 ± 7.9%) and had significant relationship with fish length and body weight. Spawning individuals had higher allometry coefficient (b) and condition factor (K) than the non-spawning individuals. The oligohaline upper Chikugo estuary provides important feeding and spawning grounds for the fish with sufficient prey abundance and turbidity maximum that seemed advantageous for feeding and spawning of N. reganius in the Chikugo estuary. We suggest that future research should emphasize on the spawning and early life ecology of the fish in order to formulate effective conservation action.

Mass budget of the sea bass (Dicentrarchus labrax) farming losses was examined. Experiments were carried out in April, September and November 2001 in tanks of 8.5 m3 containing sea bass of 1, 31 and 53 g, respectively. Samples were taken at the input and discharge points of the tank at hourly intervals over 24 h. They were later analysed for nutrient concentration, as well as particulate organic carbon and nitrogen, chlorophyll a (Chl a) and total bacterial abundance. Despite the high water supply (exchange rate: 50% h−1), NH4 concentration was significantly higher in discharge water than in input water in all three experiments independent of fish size. The same was found to hold true for PO4 for part of the day (April, November) or for the entire day (September). NO3 and SiO2 ions did not show any differences during April. Particulate organic carbon (POC) and nitrogen (PON) were higher in the discharge water in all seasons. Chl a concentration was higher in the discharge water during the entire day in September whereas bacteria presented higher counts in the output water only during part of the day in April. It was found that 5−7% of the nitrogen supplied is released into the water column as fine particulate material in the form of PON and 21−29% as NH4. A small proportion (13−16%) of supplied phosphorus (P) was released as PO4. The results provided in the present paper are useful in assessing environmental changes in water quality in the vicinity of fish farms in the Mediterranean.

A simple system was used to simulate the effect of alternating toxic (paralytic shellfish poisoning toxins) and non-toxic microalgal diets on oyster feeding behaviors and rates of toxin accumulation. These experimental conditions were meant to reflect, to some extent, the incoming and outgoing fluxes of toxic algae observed at the mouth of the Penzé estuary (Northern Brittany, France). Physiological and toxicological parameters were estimated based on fluorescence measurements recorded continuously at the outlet of each experimental tank, which contained a single oyster. Q tox, this variable describes toxin uptake in oysters, it was used (instead of the toxin ingestion rate): i) in simple graphical analyses, ii) as well as in one- and two-compartment models. Results show that toxin uptake varies widely from one individual to another and is not proportional to the concentration of toxic algae in sea water. A one-compartment model with individual fluorescence recordings as “input” data gave questionable results, however, a two-compartment model was found to effectively describe contamination kinetics in oysters. Limitations of this model as well as possible improvements are discussed.

Yellowfin tuna (Thunnus albacares) are known to preferentially occupy the surface mixed layer above the thermocline and it has been suggested that they are physiologically restricted to water temperatures no more than 8 °C colder than surface waters. However, we here report for dive data acquired from a large yellowfin tuna which demonstrate for the first time that this species is indeed capable of making prolonged dives into deep cold waters. A yellowfin tuna (134 cm fork length) caught near an anchored fish aggregating device (FAD) in the Seychelles (Western Indian Ocean) was equipped with an internally implanted archival tag and released. The fish was recaptured 98 days later. As predicted for this species, this fish spent 85% of its time shallower than 75 m (maximum thermocline depth experienced by the fish) but, over the course of the track, it performed three deep dives to 578 m, 982 m and 1160 m. Minimum ambient water temperatures recorded at these depths were 8.6 °C, 7.4 °C and 5.8 °C respectively and varied by up to 23.3 °C from surface temperatures. The fish spent 8.3% of its time in waters more than 8 °C colder than the surface layer and daily experienced a wide range of sea temperatures (mode at 15-16 °C) and of temperatures of the gut cavity (mode at 6 °C). The reason for these dives can not be known. These depths and temperatures significantly exceed those reported in the literature so far and clearly demonstrate that this species has the physiological and behavioral ability to penetrate deep cold sections of the ocean.