A new method to estimate the fraction of daily spawning females and the numbers of spawnings in Sardinops sagax in northern Chile
Gabriel Claramunt, Gustavo Herrera

A new method is proposed to estimate the fraction of daily spawning females, on a monthly basis in Sardinops sagax Jenyns in northern Chile, to trace its evolution and to be able to determine the number of spawnings in a particular season or in a year. A potentially close relationship exists between the average diameter of ovocytes of the more advanced mode (ODAM) and the weight of the ovary. The female frequency distribution, in terms of the estimated ODAM, is of the normal unimodal type. Therefore, if the mean and the standard deviation governing that distribution are known, it is possible to determine the proportions of females in specific gonad states in the population. Due to the low numbers of hydrated females in samples and consequent underestimation of the standard deviation, a value superior to 160 pm is assumed to cover the whole range of observed ODAM. In this way, an average monthly ODAM of the Sardinops sagax population represents the mean of a normal distribution with a standard deviation of 160 pm; it is thus possible to estimate that proportion of females showing an ODAM superior to 650 pm, which represents the daily fraction of monthly spawning females. For the periods August-December 1988 and August 1989 the fractions of spawning females estimated were 15.3 % and 15.7 % respectively. The incidence of postovulatory follicles for the same periods were 15.2 and 15.3 % respectively, which in some degree validates the proposed method. For the main spawning period of 1989 (June to November) it was estimated that a single female could have spawned sixteen times:

Keywords: Reproduction, daily spawning females fraction, number of spawnings, sardine, Pacific, Chile.
Contents of this volume Sci. Mar. 58(3) : 169-177 Back PDF
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