Growth Pattern, Mortality and Exploitation Rate of the Giant African Threadfin, Polydactylus quadrifilis (Cuvier, 1829) from Ebrié Lagoon (Potou Sector, Côte d’Ivoire)
Théophile Aké Bédia
Laboratoire des milieux naturels et de la conservation de la biodiversité, UFR Biosciences, Université Félix Houphouët-Boigny (Côte d’Ivoire), 22 BP 582 Abidjan, Côte d’Ivoire.
Bakari Coulibaly *
Centre de Recherches Océanologiques (C.R.O) B.P.V 18 Abidjan, Côte d’Ivoire.
Yao Aristide Konan
Laboratoire des milieux naturels et de la conservation de la biodiversité, UFR Biosciences, Université Félix Houphouët-Boigny (Côte d’Ivoire), 22 BP 582 Abidjan, Côte d’Ivoire.
Essetchi Paul Kouamelan
Laboratoire des milieux naturels et de la conservation de la biodiversité, UFR Biosciences, Université Félix Houphouët-Boigny (Côte d’Ivoire), 22 BP 582 Abidjan, Côte d’Ivoire.
Valentin N’douba
Laboratoire des milieux naturels et de la conservation de la biodiversité, UFR Biosciences, Université Félix Houphouët-Boigny (Côte d’Ivoire), 22 BP 582 Abidjan, Côte d’Ivoire.
*Author to whom correspondence should be addressed.
Abstract
The study evaluated some population parameters of Polydactylus quadrifilis within Ebrié lagoon (Potou sector). Samples were obtained using artisanal gillnet fishery from April 2004 to March 2006. A total of 741 individuals of P. quadrifilis ranged from 11 to 70 cm were examined. Population parameters were estimated where asymptotic length (L∞) was found 60 cm, growth rate (K) 0.33 per year, the longevity (T max) 9.09 years, and growth performance index (Φ′) 3.06. The length at first capture (Lc50 = 10.60 cm) was lower than the length at first maturity (Lm50 = 40 cm). Total mortality rate (Z) was calculated as 1.10 per year including natural mortality and fishing mortality. The exploitation rate (E=0.36) was found to be less than the maximum exploitation rate (E max = 0.44) and indicated that P. quadrifilis is not overexploited. The current exploitation rate should be maintained by sustainable fisheries measures including monitoring of fishing effort.
Keywords: Fisheries management, Ebrié Lagoon, Polydactylus quadrifilis, stock assessment.