Breeding, growth, mortality and yield of the mudskipper Periophthalmus barbarus (Linneaus 1766) (Teleostei: Gobiidae) in the Imo River estuary, Nigeria

We studied the reproductive biology, growth, mortality, recruitment pattern and yield-per-recruit to the fishery of the mudskipper Periophthalmus barbarus (= P. papilio) in the intertidal swamps of the Imo River estuary in the south-eastern Nigeria. Monthly variation in gonadosomatic index reveals that the males spawn once in a year from February to May and the females from March to May. The size at which 50% of the specimens matured was 10.2cm (total length) for females and 10.5cm for males while the median size at spawning was 10.8cm for females and 11.9cm for males. We collected and analysed 12 consecutive months length–frequency data using FISAT software. Fitting the seasonalized von Bertalanffy growth function to these data gave the following results: L∞=21.6cm total length, K=0.55yr−1, C=0.9, WP=0.2 of the year. Using the seasonalized catch curve procedure, the estimated instantaneous total mortality coefficient Z=4.21yr−1. The instantaneous fishing mortality coefficient F=2.86yr−1, and the instantaneous natural mortality coefficient M=1.35yr−1. Our computed exploitation rate E=0.68 showed that fishing pressure on the stock is high. This was supported by the results of our relative yield-per-recruit analysis which showed the predicted maximum exploitation level Emax=0.51 which was lower than the current exploitation rate (E=0.68).