Breeding seasonality and population dynamics of the catfish Schilbe mystus (Schilbeidae) in the Cross River, Nigeria
Twelve consecutive months length frequency data (N = 6999) and FiSAT software were used in the study of the dynamics of exploited population the catfish Schilbe mystus in the Cross River Nigeria. Variation in monthly mean gonadosmtic index showed two peaks, March and September and this indicates that the species spawned twice in a year. Fitting the seasonalized von Bertalantffy growth function to our length frequency data gave the following growth parameters: L∞ = 38 cm, k = 0.33 y-1, C = 0.42 and WP = 0.96. The seasonalized length converted catch curve procedure gave the instantaneous total mortality coefficient Z = 2.97 y-1, the instantaneous natural mortality coefficient M = 0.81 Y-1, the instantaneous fishing mortality coefficient F = 2.16 y-1 and the current exploitation rate E = 0.73. This high value of E points to the high fishing pressure on the stock. The analysis of probability of capture of each length class showed that the length at first capture Lc 28.67cm. The predicted maximum exploitation rate of Emax = 0.59. This stock was deemed overexploited because E>Emax. Relative yield isopleths were used to demonstrate the response of relative yield per recruit of the fish to variation Lc and E. Suitable management procedure must be instituted to avoid the collapse of the fishery.