Population structure, growth, mortality and exploitation rate of manjuba, Anchoviella lepidentostole (Pisces, Engraulidae), stock at Ribeira de Iguape River, Southern São Paulo State, Brazil, from 1993 to 1996

Abstract

Samplings of Anchoviella lepidentostole ("manjuba") Fowler, 1911, were done from 1993 to 1996 at Ribeira de Iguape River, Southeastern São Paulo State. Population structures were identified and the growth parameters as well as the exploitation rates were estimated. It was realized that sexual ratio is around 1:1, but when fishing season is ending (in March or April) male individuals are minority and the capture tends to fall upon younger groups. The growth curve when all the observed values are considered presents L∞ = 148.3 mm and K= 0.83. It was verified the existence of two cohorts, considered as Summer's and Winter’s, this one having lower growth rates. Each cohort has showed three age classes, appearing a superposition of curves relative to the longer individuaIs, which indicates a compensation on the differences in growth parameters, along the cycle of Iife. The coefficients of mortality due to fishing as well as the exploitation rates, in comparison with those ones from one decade ago, were major, despite the lower levels in production. This fact indicates a non-response of the stock for increases in fishing efforts.