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.
Highlights
Chrysichthys nigrodigitatus known as silver catfish, is a highly valued food fish occurring in several African waters
Uyoh et al (2020) reported that Chrysichthys nigrodigitatus of the Cross River has very low genetic diversity and that such low genetic diversity can lead to population eradication in the face of environmental variability
Population dynamics describes the pathways in which a given population grows and shrinks over time as controlled by birth, death and emigration or immigration (King, 1995).Major causes of death are fishing by humans and natural mortality caused by environmental factors including climatic factors like temperature and Daniel Ama-Abasi, Institute of Oceanography, University of Calabar, Calabar, Nigeria
Summary
Chrysichthys nigrodigitatus known as silver catfish, is a highly valued food fish occurring in several African waters. It is among the dominant fish species of commercial importance. Edide (2017) reported that in the Cross River system, C. nigrodigitatus is the most important single species of commercial significance occurring all year round with peak abundance in the rainy season, and that. Uyoh et al (2020) reported that Chrysichthys nigrodigitatus of the Cross River has very low genetic diversity and that such low genetic diversity can lead to population eradication in the face of environmental variability.
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