A methodology for visual estimation of abundance applied to flyingfish stocks

Une méthode d'estimation de l'abondance des stocks de poissons volants est proposée. Elle est basée sur des comptages, regroupés par intervalles de distance réguliers, de poissons s'envolant à l'approche d'un bateau de recherche effectuant des radiales prédéterminées. En cela la méthode s'apparente aux évaluations de stock par écho-intégration. Durant les campagnes, on collectera diverses variables (biologiques, physiques et climatiques) pouvant influencer directement ou indirectement les estimations d'abondance ou la répartition de la ressource. La méthodologie d'observation (directe et avec caméra) et d'analyse des données est décrite, ainsi que l'équipement nécessaire afin de saisir directement sur support informatique un maximum de données. (Résumé d'auteur

Choix d'une unité d'effort de pêche pour les flottilles sardinières sémi-industrielles et artisanales au Sénégal

Different catches per unit of effort available for industrial and artisanal sardinella fisheries of Senegal have been analysed and compared in order to determine whether they are acceptable indices of abundance. Among the four units of fishing effort studied (total number of sets, number of trips, time spent on fishing ground, searching time), the first and the second seem inadequate in the studied fleets. The two other units, particularly the searching time, allow the calculation of catches per unit of effort which best reflect variations in abundance, although they are not completely free of usual deficiencies

Влияние предварительного деформирования на ударную вязкость образца Шарпи при разрушении

Предложен подход к оценке величины ударной вязкости образца Шарпи на верхнем шельфе в зависимости от степени предварительного пластического деформирования металлопроката. Выполнен анализ полученных аналитических зависимостей и определены основные параметры, характеризующие их изменения. Предложена простая инженерная зависимость позволяющая оценить изменение ударной вязкости образца Шарпи на верхнем шельфе в зависимости от степени пластического деформирования при изготовлении и монтаже элементов металлоконструкций.An approach is proposed to evaluation of upper shelf impact toughness of a Charpy sample depending on the degree of plastic pre-deformation of metal rolled stock. The derived analytical dependencies have been analyzed, and the main parameters have been determined, characterizing their change. A simple engineering dependence is proposed, which allows evaluation of the change of upper shelf impact toughness of a Charpy sample depending on the degree of plastic deformation in fabrication and assembly of metal structure elements

Analysis of vessel influence on spatial behaviour of fish schools using a multi-beam sonar and consequences for biomass estimates by echo-sounder

Biases in the measurements of spatial distribution of fish schools and their consequences for school biomass estimates during conventional acoustic surveys are mainly due to vertical and lateral avoidance of the vessel. In this paper, we quantify school avoidance during an acoustic survey carried out from 10 to 29 May 1994 in the Catalan Sea. From a lateral multi-beam sonar the geometric characteristics (depth, length, width, height, surface, and volume) of 1268 schools were obtained. The 60 beams (1.5° X 15°) of the sonar scanned a vertical plane from 0° to 90°, perpendicular to the vessel path within a range of 100 m. Within this plane, the projected area ensonified by the echo-sounder used aboard for acoustic evaluation was evaluated to simulate a comparison between the sonar and the echo-sounder. The results have enabled us to improve our knowledge on the vertical and lateral avoidance patterns of schools in relation to their size, external structure, and their position in the water column, and to quantify the vessel influence on biomass estimated by echo-sounder. (Résumé d'auteur

Diel variability of school structure with special reference to transition periods

Pelagic fishes generally dispers at dusk and aggregate in schools at dawn. The dynamics (duration, variation in school number, and characteristics) of these two behavioural processes have been studied during a 26 h survey in a small area of high fish abundance in the Catalan Sea (Spain). The dynamics of aggregation and dispersion were investigated using a dual-beam vertical echo-sounder (BioSonics) connected to a special school integrator software package (INES-MOVIES-B) which estimates school parameters in terms of size, geometry, and density. This study shows that, during the night, fish dispersion is limited and schools can still be observed. They are characterized by a highly skewed distribution of the cross-sectional area (many small schools plus a few medium and large schools), low values of packing density and biomass, and irregular shape, while during the day there are only a few schools which have a lower variability of the area, high values of packing density, and a more regular shape. The dynamics of schooling are different between dawn (fast aggregation) and dusk (slower dispersion). (Résumé d'auteur