2011 - INIDEP Informe Técnico Nro 79-83

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Browsing 2011 - INIDEP Informe Técnico Nro 79-83 by Author "Hansen, J.E."

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    Parámetros biológicos relevantes para las pesquerías de anchoíta argentina (Engraulis anchoita). Estimaciones resultantes de reunir datos de campañas de investigación (1993 a 2008) y de muestras de capturas comerciales (1986 a 2009)
    (INIDEP, 2011) Hansen, J.E.
    The aim of this paper was to accurately estimate population parameters of northern (“bonaerensis”, latitude < 41° S) and southern (“patagonic”, latitude 41° S) Argentine anchovy stocks and to describe some aspects of their behaviour. The research surveys allowed to obtain data on length, total weight, sex, maturity and age of 27,853 specimens of the northern and 12,787 of the southern stocks. Besides, 20,717 age determinations stemmed from commercial landing samplings of the northern stock were established. Sex proportion in the northern population was 0.50 : 0.50; the southern showed a slight predominance of males (0.52 : 0.48). Data derived from cruises and commercial landings showed statistical differences in the growth ratio of the northern stock where mean size at ages 0-2 proved to be slightly higher in landings; the opposite was observed about ages 5-6. On the other hand, research data showed similarity in mean size at age of both stocks, used to fit a unique von Bertalanffy growth function (L = 194.62; K = 0.456; t0 = -0.86). In the October surveys on the northern anchovy stock higher mean weight at size and age than in December cruises on the southern stock were observed, which resulted in significant differences between both length (mm)-weight (g) relations described, respectively, by equations W = 1.867 * 10-6 * L3.254 and W = 1,467 * 10-6 * L3,290; likewise, a higher asymptotic weight was calculated for specimens of the first group (53.36 g vs 47.47 g). Estimates of natural instantaneous mortality rates, carried out using different methods available in the literature, allow to suggest values M = 1.01 for the northern and M = 0.98 for the southern populations. A marked discrepancy between both stocks was observed in their capacity to reach sexual maturity, the northern group being precocious (L50% = 98,0 mm; t50% = 0,58 years vs 119,2 mm and 1,14 years). The size of specimens in the shoals of both populations, mainly in the southern, was homogeneous whether at day or night time. The preferential spawning period, that ranged 4-10 pm, was common to both stocks; nevertheless, females with hydrated oocytes were more frequent in the samples taken from the northen population, which indicates shorter periods between batch spawning.