Population parameter estimates for Chrysichthys auratus and C. nigrodigitatus (Pisces: Claroteidae) in Lake Volta, Ghana

• Published in: Fisheries research 2002, Vol.54 (2), p.267-277
• Main Authors: Ofori-Danson, P.K, de Graaf, G.J, Vanderpuye, C.J
• Format: Article
• Language: English
• Subjects: Agnatha. Pisces; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Biological and medical sciences; Chrysichthys; Chrysichthys auratus; Chrysichthys nigrodigitatus; Claroteidae; Demecology; Fundamental and applied biological sciences. Psychology; Growth; Lake Volta; Mortality; Pisces; Vertebrata
• ISSN: 0165-7836; 1872-6763
• DOI: 10.1016/S0165-7836(00)00292-7

Estimation of population parameters of two commercially important claroteids ( Chrysichthys auratus and C. nigrodigitatus) in lake Volta were obtained from length composition data compiled in 1995 and 1996. The von Bertalanffy growth constants for C. auratus were computed as L ∞=31.0 cm SL, K=0.60 yr −1 and t 0=−0.12 yr with derived growth performance index ( ϕ′=2.76). Corresponding estimation for C. nigrodigitatus were L ∞=44.5 cm , K=0.65 yr −1 , t 0=−0.22 yr and ϕ′=3.12. The two species live for about 5 years and attain at least 50% of the asymptotic length at the first age class. The growth patterns determined by the growth performance index ( ϕ′) were higher for C. nigrodigitatus than for C. auratus of similar sizes. Total mortality rate, Z, for the fish ranging 6.0–30.0 cm SL was estimated as 2.63 yr −1 and the natural mortality rate, M, estimated as 1.30 yr −1 with average fishing mortality, F, calculated as 1.33 yr −1. From the mortality estimation the exploitation ratio ( E= F/ Z) for C. auratus was 0.51. Mortality rate estimates for C. nigrodigitatus were Z=3.77 yr −1 , M=1.24 yr −1 and F=2.53 yr −1 and exploitation ratio, E, calculated as 0.67 which is indicative of over-fishing. The management implications of the results to the fishery are discussed and suggestions made for sustainable exploitation of the stocks.