Ecology and population dynamics of silver catfish, <I>Chrysichthys nigrodigitatus</I> (Siluriformes: Claroteidae), of the Cross River, Nigeria

Abstract

Chrysichthys nigrodigitatus forms the most commercially important freshwater single species fishery in the Cross River, Nigeria. Studies were  conducted on the dynamics of the exploited population of the species and the influence of rainfall on its catch rate. The objectives were to assess the level of exploitation and impacts of rainfall on its catch rate. A time series of length frequency and meteorological parameters was conducted. Length frequency data were analyzed using FiSAT software to estimate population parameters. The asymptotic length, Lı was 105 cm, growth constant (K) was 0.68 year^-1, total mortality (Z) was 2.48 year^-1, Natural mortality (M) was 0.99 year^-1 and fishing mortality (F) was 1.49 year^-1. The exploitation rate was 0.60 year^-1, indicating overfishing. Natural mortality accounted 40% of the total mortality, presenting a worrisome trend in the fishery. There was a correlation between rainfall and catch rate, which increased at the onset of rains but decreased at the peak of the rains due to increased depth of the river. For management purposes, it is recommended that the fishing effort should be reduced by the regulation of the number of boat-days; for conservation, domestication of the species should be adopted as an adaptation to climatic influence.

Keywords: Freshwater Catfish, Fishing Mortality, Exploitation Rate, Overfishing, Rainfall Impact, Niger Delta.