DOI: 10.14798/73.3.834
Bibliography
POPULATION DYNAMICS OF Chrysichthys nigrodigitatus (Lacépède, 1803) IN LOWER CROSS RIVER, NIGERIA
2015, 73 (3) p. 103-114
James Philip Udoh, John Etitigwun Ukpatu, Okon Michael Udoidiong
Abstract
Silver catfish Chrysichthys nigrodigitatus (Lacépède, 1803) constitutes the main fishery offering diversified livelihood to the artisanal communities in southeast Nigeria and has been heavily fished over time without attempts at conservation. This study was conducted to estimate the current population parameters needed for its rational exploitation. Estimates of growth and mortality of catfish in the Lower Cross River, Nigeria, were obtained from length-frequency data of 6637 individuals collected on monthly basis from November 2011 to October 2012. The estimated von Bertalanffy growth function (VBGF) parameters were: asymptotic length L∞ = 120.23 cm total length, growth coefficient K = 1.50 year-1 and age at zero length, t0 = 0.0 years. The amplitude of growth oscillations C = 0.75, winter point WP = 0.50 or 1 July and growth performance index, φ = 4.336. The rates for natural, fishing and total mortalities were: M =1.58, F = 2.55 and Z = 4.31 per year, respectively. This study reveals growth overfishing and threat of extinction of C. nigrodigitatus in the Lower Cross River system characterized by heavy fishing pressure on the length group 34.5 - 94.5 cm TL, reduced life span from 5 to 2 years, change from a slow growth pattern typical of siluroids to a fast one with current exploitation rate, Ecur (F /Z) = 0.62, about 15.8% higher than the allowable maximum exploitation rate, Emax = 0.522. In order to restore ecosystem health, a community-based multisectoral stakeholder consortium invested with limited equity and access for exploiting the fishery in tandem with its bio-ecological dynamics should be encouraged. Other policy instruments such as periodic prohibition of fishing, controlled pricing and public education are recommended for the sustainability and conservation of the fisheries.
Keywords
age, growth, mortality, species extinction, stock assessment, yield isopleths