Manual of acoustics theory and application to the biosonics-system for target strength measurement

At the end of 1996, a training course in acoustics was performed. Acoustics, as an important tool in fishery assessment, is destined to be continued by Indonesian scientists, after the closure of the PELFISH Project. This project, sponsored by the European Union, Indonesia, and France took place from 1991 to 1995, and twenty acoustic cruises in the Java Sea and the surrounding areas were achieved. To fulfill the aim of the PELFISH Project, besides the electronic equipment, this training was therefore indispensable to use it. This paper recalls the basics of acoustics, all about the scientific apparatus and their adjustments, the procedures of data acquisition and their post processing. (Résumé d'auteur

Quantifying the interplay between environmental and social effects on aggregated-fish dynamics

Demonstrating and quantifying the respective roles of social interactions and external stimuli governing fish dynamics is key to understanding fish spatial distribution. If seminal studies have contributed to our understanding of fish spatial organization in schools, little experimental information is available on fish in their natural environment, where aggregations often occur in the presence of spatial heterogeneities. Here, we applied novel modeling approaches coupled to accurate acoustic tracking for studying the dynamics of a group of gregarious fish in a heterogeneous environment. To this purpose, we acoustically tracked with submeter resolution the positions of twelve small pelagic fish (Selar crumenophthalmus) in the presence of an anchored floating object, constituting a point of attraction for several fish species. We constructed a field-based model for aggregated-fish dynamics, deriving effective interactions for both social and external stimuli from experiments. We tuned the model parameters that best fit the experimental data and quantified the importance of social interactions in the aggregation, providing an explanation for the spatial structure of fish aggregations found around floating objects. Our results can be generalized to other gregarious species and contexts as long as it is possible to observe the fine-scale movements of a subset of individuals.Comment: 10 pages, 5 figures and 4 supplementary figure

Proceedings of acoustics seminar AKUSTIKAN 2

The detection and the reverberation measurement of the fish by acoustics allows their behaviour, distribution and structures to be analyzed. All these investigations are mainly based on a relative evaluation of densities. The method of echo-integration also allows the abundance to be quantified. It then necessitates knowing accurately the acoustic performances of the apparatus and the definition of a weight conversion coefficient to apply on the relative data. The Ines-Movies system, used during the acoustic surveys of the PELFISH Project, consists of a calculation procedure with a conversion coefficient. After determination of the #Decapturus russelli$ reverberation index (or TS), in cage this coefficient has been calculated. The accuracy of evaluations resulting from such an index depends particularly on the TS one. But another parameter has to be taken into account ; this is the adjustment of threshold during the prospecting. Even with a controlled adjustment of this latter, the conversion of relative integrated values of the Java Sea shows that the evaluations obtained in this way do not correspond to the richness of the area. According to fishing techniques, the level of commercial Ines-Movies system, allows to better adjust the threshold for evaluation of the targets, taking into account the reverberating surrounding conditions. (Résumé d'auteur

Proceedings of acoustics seminar AKUSTIKAN 2

Using acoustics for biomass evaluation, the back scattering cross section of species has to be determined to convert the data into weighted values. During the cruises of the EU Project "Java Sea Pelagic Fishery", TS measurements on 3 pelagic fishes of economic importance : #Decapterus russelli, #Selar crumenophthalmus, and #Rastrelliger kanagurta$ were carried out, using a BioSonics dual beam echo-sounder at a frequency of 120 kHz. The observations on single or multiple targets in a cage, revealed a large dispersion of the responses, even in the same experiment. These results are discussed and compared with Johannesson's (Anonymous, 1984) in the same area. (Résumé d'auteur