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

We studied the breeding biology, growth, mortality, recruitment pattern and yield per recruit of a freshwater siluroid catfish (Schilbe intermedius) i n the Cross River, Nigeria. Monthly variation in mean gonadosomatic and mea n condition indices shows that the species breeds twice in a year (March an d 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 Bertalanf fy growth function to our length-frequency data gives the following growth parameters: L-infinity = 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 instant aneous natural mortality coefficient M was 0.81 yr(-1) while the instantane ous fishing mortality coefficient F was 1.04 yr(-1), giving the current exp loitation rate E = 0.56. From the analysis of probability of capture of eac h 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 = 0.53. The current exploitation rate E is more than this predic ted maximum E-max. Thus, the species is on the verge of being overexploited . (C) 1999 Elsevier Science B.V. All rights reserved.