Revista de Investigación y Desarrollo Pesquero 1986 Nro 5

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Browsing Revista de Investigación y Desarrollo Pesquero 1986 Nro 5 by Subject "Age composition"

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    Estudios de distribución de la anchoíta (Engraulis anchoita) en un área de extensión reducida. I. Densidades mínimas de muestreo para la estimación de algunos parámetros poblacionales
    (Mar del Plata: Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), 1986) Gru, D.L.; Hansen, J.E.
    Results of a research cruise carried out to estimate some biological parameters of anchovy (Engraulis anchoita), during the major spawning season, were analyzed in order to determine the minimum number of samples required to obtain unbiased values. Twelve samples of fishes were taken within an area of 607 nm². Size (total length)distributions, slope of the length-weight relationship, sex ratio and age population structure were considered. Results suggest that those parameters should be estimated by eight or more samples (corresponding to 76 nm² each).
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    Resultados de una campaña de investigación sobre la anchoíta (Engraulis anchoita) del sector bonaerense en el otoño de 1983. Distribución, abundancia y algunos aspectos biológico-pesqueros
    (Mar del Plata: Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), 1986) Hansen, J.E.; Gru, D.L.; Perrotta, R.G.
    An extensive area of the continental shelf -between 37°20' and 34°40'S - was reviewed through hidroacoustical methods in order to evaluate the anchovy biomass. Within the area of highest concentration, further data on anchovy abundance were recorded, and fish samples were taken. Large anchovy shoals were located at about 170 nm from Mar del Plata, mainly in zones with sharp changes in oceanographic conditions. The distribution of the species was not uniform, but "contagious", and the log-normal distribution provided the best fit for the echo-integrator recorded data. The biomass was estimated at 1,061,727 tons (Confidence limits in between 921,010 and 1,223,930 tons). Some parameters of the population were estimated, such as: lenght-weight relationship, von Bertalanffy growth curve constants, sex ratio, maturity, and age composition. Taking into account a calculated naturaly mortality rate of M= 0.85, a Maximum Sustainable Yield at about 451,000 tons was estimated (Confidence limits at about 520,000 and 390,000 tons).