Browsing by Author "Viñas, M.D."

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    La caballa (Scomber japonicus) y las condiciones del ambiente en el área "El Rincón" (39°40'-41°30' S) del Mar Argentino. Septiembre, 2000
    (Mar del Plata: Instituto Nacional de Investigación y Desarrollo Pesquero, 2003) Perrotta, Ricardo G.; Viñas, M.D.; Madirolas, A.; Reta, Raúl; Akselman, Rut; Castro Machado, Federico; Garciarena, A. David; Macchi, Gustavo J.; Moriondo Danovaro, Paula; Llanos, V.; Urteaga, J.R.
    Between September 1st and 6th a research cruise was carried out in the Buenos Aires shelf area of "El Rincon" 39°40'-41°30'S, Argentine Sea SW Atlantic. The total area studied was 2,527.8 nautical mile2. Knowledge of the commercial fleet location at the time of the survey allowed to intensify sampling in a 'miniarea' of 52,8 nautical mile2. The acoustic assessment of chub mackerel (Scomber japonicus) biomass was 49,511.9 t, 94 of which corresponded to this last area. Fish samples coming from fishing trawls included only adult individuals of 240-460 mm total length (TL) and ages ranging 2-11 years. The limit age was estimated at 13 years and natural and total mortality rates at 0.23 and 0.54, respectively. Oceanographic conditions were those typical of the winter season, characterized by the vertical homogeneity of the water column in temperature and salinity. The isotherms and isohalines distributed parallel to the 50 m isobath with values progressively decreasing from the coast towards the slope. Salinity values allowed to detect two hydrographic regimes: that of the San Matias Gulf 33.8-34.4 located to the West and covering more than half of the study area and the one of the Shelf Waters 33.5-33.79 occurring towards the East. A positive gradient in chlorophyll a concentration was observed in N-S sense and from the coast towards the shelf break. The highest densities of phytoplankton, with dominance of diatoms, were observed in the southern sector. Low concentrations of Alexandrium tamarense and Prorocentrum minimum, two potentially noxious dinoflagellates, were detected. The highest zooplankton biomass associated to the highest salinity values and salinity gradients, represented mostly by Calanoides cf. carinatus, was also detected in the southern sector. The western sector, influenced by the San Matias Gulf regime and characterized by high densities of both, phytoplankton and zooplankton, may constitute a potentially favourable feeding ground for chub mackerel.
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    Variaciones de la abundancia numérica y biomasa del zooplancton de red en el Golfo San Jorge (año 1985)
    (Mar del Plata: Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), 1987) Pérez Seijas, G.M.; Ramirez, F.C.; Viñas, M.D.
    A study was made on numercial and biomass variations of the zooplankton of the San Jorge Gulf (Argentina), based on samples from five cruises performed during 1985. The sampling was included within a proagramme for the biology and fishery evaluation of the shrimp Pleoticus muelleri. San Jorge, a large gulf of the northern patagonian shelf, comprises major fishery activities. Some fish species of economical importance depend on copepods for their feeding, like anchovy (Engraulis anchoita) or partially on middle-size plankters, like mackerel (Scomber japonicus). As a way for determining the trophic disponibility at the gulf, a study was made in order to express the numerical abundance of copepods, euphausiids and amphipods and other items of lesser importance, as well as their total biomass.