26 research outputs found
Mesures in situ des index de réflectivité à l'aide d'un écho-sondeur type "Dual beam" (129 kHz, BioSonics) et chalutage d'identification spécifique : Venezuela orientale : mission Varget 2/1996-99 (Orstom-Flasa-CroDT)
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
Marine mammal depredation and pelagic longline fishery : second trail to assess the efficiency of a scaring mitigating device in Saint-Paul Bay (Reunion Island)
Marine mammal depredation and pelagic longline fishery : assessment of the efficiency of a scaring mitigating device in Saint-Paul Bay (Reunion Island)
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
Mesures in situ des index de réflectivité à l'aide d'un écho-sondeur type "Dual beam" (129 kHz, BioSonics) et chalutage d'identification spécifique : Venezuela orientale : mission Varget 2/1996-99
Mesures in situ des index de réflectivité à l'aide d'un écho-sondeur type "Dual beam" (129 kHz, BioSonics) et chalutage d'identification spécifique : Venezuela orientale : mission Varget 2/1996-99
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