Growth and mortality, recruitment and yield of the fresh-water shrimp, Macrobrachium völlenhovenii, Herklots 1851 (Crustacea, Palaemonidae) in the Fahe reservoir, Côte d'Ivoire, West Africa

Abstract

We studied the growth, mortality rates and recruitment pattern of an exploited fresh-water shrimp ( Macrobrachium völlenhovenii) population in the Fahe reservoir of the San-Pedro River, Côte d'Ivoire using 12 consecutive months (January to December 1995) length–frequency samples and FISAT software (which incorporates both the ELEFAN and LSFA programs). A fit of the seasonalized von Bertalanffy growth equation to the length–frequency data gave the following results: L ∞=18.0 cm total length, K=0.91 year −1, C=0.92, WP=0.44 of year (i.e. July), and an R n value of 0.45. We also estimated the instantaneous total mortality coefficient Z=3.69 year −1 through the seasonalized length-converted catch curve procedure. The instantaneous natural mortality coefficient M was 1.97 year −1 while the instantaneous fishing mortality coefficient was 1.72 year −1. An exploitation rate E of 0.47 implies that the stock is almost optimally exploited. The results of our yield-per-recruit analysis lend further credence to this assertion. The distribution of juveniles and ovigerous females in the samples show that there is one reproduction peak in August and one recruitment peak from September to November. We back-projected our length–frequency data set on to an arbitrary one-year scale. The results also show that there is one recruitment in a year.