The Influence of Hydroregime on Catch, Abundance And Recruitment of the Catfish, Chrysichthys Nigrodigitatus (Bagridae) and the Bonga, Ethmalosa Fimbriata (Clupeidae) of Southeastern Nigeria's Inshore Waters

Abstract

This paper investigates the relationship between the hydroclimatic parameters (rainfall and flood index) and the catch, stock abundance and recruitment of the catfish, Chrysichthys nigrodigitatus (Bagridae) and the bonga, Ethmalosa fimbriata (Clupeidae) of southeastern Nigeria's inshore waters. For C. nigrodigitatus, most peaks in the mean biomass $(\Delta \% {\bar B})$ and recruitment $(\Delta \% {\bar R(n)})$ curves occurred during the 'wet' years, i.e., years for which the percentage deviations of rainfall $(\Delta \% \overline {{RF}} )$ and flood index $(\Delta \% \overline {{FI}} - 1)$ from their means remained above their averages. Catch and abundance respectively showed good positive linear correlation with the flood index. E. fimbriata behaved differently; some peaks in the $\Delta \% {\bar B}$ and $\Delta \% {\bar R(n)}$ curves occurred in the 'wet' and some in the 'dry' years; and there was no correlation between the annual catch of bonga and either the rainfall or the flood index. The hypothesis, that linear relationships exist between the interannual variations in the hydroregime and the yearly fluctuations in the catch and population structure of some coastal and estuarine fishes, holds true for the catfish, C. nigrodigitatus, but not for bonga, E. fimbriata.