The dynamics of an exploited population of a siluroid catfish ( Schilbe intermidius Reupell 1832) in the Cross River, Nigeria

Abstract

We studied the breeding biology, growth, mortality, recruitment pattern and yield per recruit of a freshwater siluroid catfish ( Schilbe intermedius) in the Cross River, Nigeria. Monthly variation in mean gonadosomatic and mean condition indices shows that the species breeds twice in a year (March and September). We used 12 consecutive months length–frequency data together with FiSAT software to study the population dynamics of this catfish which is exploited by artisanal fishermen. Fitting the seasonalized von Bertalanffy growth function to our length–frequency data gives the following growth parameters: L ∞=27.5 cm total length, K=0.29 yr −1, C=0.5, WP=0.46. Using the seasonalized length converted catch curve, we estimated the instantaneous total mortality coefficient Z as 1.85 yr −1. The instantaneous natural mortality coefficient M was 0.81 yr −1 while the instantaneous fishing mortality coefficient F was 1.04 yr −1, giving the current exploitation rate E=0.56. From the analysis of probability of capture of each length class we estimated the length at first capture L c to be 10.9 cm. The relative yield per recruit analysis predicted the maximum exploitation rate E max=0.54. The current exploitation rate E is more than this predicted maximum E max. Thus, the species is on the verge of being overexploited.