Today's increase of functions, improvement of performances, and cost reductions required on an agile electronically scanned antenna, drive researchers to develop an innovative antennas’ concept in order to deal with the proposed challenge. In this context, this article describes and demonstrates an experimental prototype to show the reliability and efficiency of the electromagnetic band gap (EBG) matrix antenna theoretical aspect, for beam forming and beam steering applications. The originality of this work is the antenna itself which constitutes the subject of an accepted national and international patent. In fact, the proposed antenna is based on the equivalent radiating surface approach and used special EBG antennas called “pixels” to overcome some of the array approach defects. The antenna has demonstrated different electromagnetic behaviors, such as low mutual coupling, high gain preservation for high scanning angles values, etc.

We investigate here the central limit theorem of the increment ratio statistic of amultifractional Brownian motion, leading to a CLT for the time varying Hurst index. Theproofs are quite simple relying on Breuer–Major theorems and an original freezingof time strategy. A simulation study shows the goodness of fit of thisestimator.

The Chilean jack mackerel (Trachurus murphyi) is one of the mostimportant exploited fish populations in the world. Its area of distribution covers thesub-tropical waters of the South Pacific Ocean, from South America up to New Zealand andeven Australia. It is subject to high variations in biomass, with annual world catchesvarying from less than 0.5 to almost 5 million tonnes. Management of this species and itsfishery requires a correct understanding of the population structure. Although severalhypotheses have been proposed, suggesting that there are up to four independentpopulations, genetic analysis indicates only a single population in the South PacificOcean. We consider the two most probable structures for this population: a “patchypopulation”, where all the fish belong to a single population that expands and contractsdepending on the biomass; and a metapopulation, where a source population creates severalsubpopulations that can remain independent during prolonged periods, depending on theenvironmental conditions. We studied the conditions for these hypotheses to representreality, especially the demographic structure and existence of different spawning areas.Using knowledge obtained from fisheries and acoustic surveys, we show that if we applytheir definitions strictly, neither of the two hypotheses can be fully rejected.Nevertheless, some particular spatial characteristics observed recently between thePeruvian and Centre-South Chilean parts of the distribution lead us to conclude that themetapopulation definition is likely to better describe the stock. The consequences of eachpopulation structure for fisheries management are listed, showing that the metapopulationhypothesis represents a safer definition for stock assessment. We conclude that T.murphyi can be described as a metapopulation, but also that the definitionsproposed in the literature on metapopulations are not fully adapted to pelagic fishpopulations with a basin-scale distribution range, and suggests specific research thatcould be done in this field.

Fisheries management now extends from the stock to the ecosystem. The foundation for fisheries management on an ecosystem basis must lie in appropriate modelling of the ecosystems. A prerequisite for such models requires data on the two interactive components of the ecosystem: the biotope (physical environment), and the community of living species. In this context, acoustics become essential, as this tool can provide qualitative and quantitative data on various communities of species, and furthermore allows the seldom-attainable study of their interactions. In fact, acoustics allow the monitoring of entire communities, from plankton to large predators, as well as certain aspects of the physical environment, such as substratum characteristics. Acoustics have been used during the last two decades mainly to provide fishery-independent estimates of stocks. The intention of this paper is to promote the use of acoustics for studying marine ecosystems and to encourage the emergence of new generations of ecosystem models. As an example of integrative research based on acoustic data, we will present the approach and the results of a scientific programme (ECOTAP) carried out to study the tuna pelagic ecosystem in French Polynesia. We then discuss the use of acoustics as a tool for ecosystem-based studies and management.

Eighty-seven two-hour acoustic surveys (radius 0.8 nautical mile, vertical range 0–500 m) around 17 fish aggregating devices (FADs) were conducted in French Polynesia between December 1995 and February 1997. Associated tuna densities were calculated using two different techniques: echo counting when the fish had sufficient distances from each other and echo integration when the fish swam close together (in schools). No acoustic detection of tuna was observed during 27 of the 87 surveys, representing 81 % of all the nocturnal surveys and 15 % of the diurnal ones. The 60 other surveys showed three different classes of aggregations: (1) ‘deep scattered fish’, observed 45 times, (2) ‘intermediate scattered fish’, observed 16 times, and (3) ‘shallow schooling fish’, observed 16 times. Sometimes aggregations of different classes were observed beneath the same FAD. The size of the fish inside the aggregations (determined from target strength values), the distance between the individuals, and the depth of the fish all decreased from ‘deep scattered fish’ to ‘shallow schooling fish’ (100–300 m for ‘deep scattered fish’, 50–150 m for ‘intermediate scattered fish’, and above the depth of 50 m for ‘shallow schooling fish’). Fish densities also varied according to the class of aggregations: 7.3, 26, and 801 fish per km3 on average for ‘deep scattered fish’, ‘intermediate scattered fish’, and ‘shallow schooling fish’, respectively. The highest densities were observed during daytime, while night-time observations indicated a variety of situations, from the absence of individuals to large amounts of fish.

A fuzzy logic model of tuna behaviour near Fish Aggregating Devices (FADs) was developed to reproduce individual differences in horizontal movements observed from ultrasonic telemetry experiments. In this model, the behaviour of an individual is based on its surrounding environment (FADs and prey) and on its internal state (stomach fullness), which depends on its recent past actions. Internal sensors are used to determine the motivation of the fish, combined with external sensors, this determines its movements. Sensory information and motivation are modeled using fuzzy sets. A FAD attracts an individual when it is located within the FAD’s range of influence. The time spent near a FAD depends on the feeding motivation of the fish and on its surrounding environment. If the fish is not hungry, it stays near the FAD. Otherwise, the fish has to forage in order to eat, and might therefore leave the FAD if no prey is available in its vicinity. By varying the environmental conditions near FADs, the model reproduces the different horizontal movement patterns observed for tunas. The model is then extended to allow multiple individuals to co-exist, each individual modeled through the above behavioural model, without any direct or indirect interactions between them. This way, we study the effects of individual behaviour on tuna aggregation near FADs. We find that the model predicts the temporal dynamics of aggregation around FADs exhibited by tunas. By examining the effects of several FAD network models on the aggregation, we also estimate optimal spatial arrangements of FADs.

The behaviour and spatial distribution of tuna, aggregated beneath fish aggregating devices (FADs), have been studied through ultrasonic tagging experiments but, surprisingly, very few studies on FADs have used underwater acoustic devices. We present techniques, and their limits, incorporating a scientific echo sounder connected to a split-beam transducer to observe and characterise tuna aggregations around FADs, and propose a general approach for future studies. Experiments were conducted in French Polynesia between December 1995 and February 1997. Two methods, echo-counting and echo integration, were used. Echo-counting is possible when individual fish are sufficiently scattered so that each target can be discerned. On the other hand, echo integration can be used with both scattered and aggregated fish schools. The knowledge of tuna target strength is useful for separating targets for echo-counting, and essential for obtaining absolute estimates of densities by echo integration. Sonar performances and settings should be considered when choosing the most suitable method to determine fish density or assessing spatial structure of a tuna aggregation. These techniques allow one to study an entire tuna aggregation, its behaviour in space and time at very fine time–space scales (about a nautical mile and over a few hours), and open up a new scientific field to study the spatial structure and behaviour of tuna aggregations around anchored or drifting FADs.