Population Dynamics of Chloroscombrus Chrysurus and Decapterus Punctatus in Coastal Waters of Ghana

Abstract

Carangids are considered as commercially important fish species in Ghana. In recent times, there has been a decline in Ghana’s pelagic stock which includes carangids. The purpose of the study was to assess the population dynamics of some common commercially important carangid stocks in the coast of Ghana to inform management decisions. The study was conducted specifically in the Tema fishing Harbour, the Elmina landing site and the Albert Bosomtwe Sam fishing Harbour in Ghana from November, 2020 to June, 2021. Length- frequency data of fish samples were used to calculate the growth and mortality parameters as well as the exploitation ratio. The growth parameters assessed for Chloroscombrus chrysurus and Decapterus punctatus were; asymptotic length (L∞) = 28.9 and 21.4 cm standard length, growth rate (K) = 0.38 and 0.55 per year, growth performance index (ɸ) =2.50 and 2.40, theoretical age at birth (to) = - 0.23 and -0.08 respectively. The Z/K ratio were 7.26 and 4.51 respectively, indicating that the stock is mortality dominated. Total mortality (Z) was estimated at 2.76 and 2.48 per year, while natural mortality (M) was 0.67 and 1.03 per year and fishing mortality (F) at 2.09 and 1.45 per year respectively. The estimated fishing mortality (F) was found to be greater than the natural mortality. Further, the current exploitation rate (E) was calculated as 0.75 and 0.58, portraying over exploited stock. The length at first maturity (Lm50), was estimated at 13.9 cm and 14.1 cm for male and female Chloroscombrus chrysurus and 14.7 cm and 12.6 cm for male and female Decapterus punctatus. The length at first capture (Lc50) was obtained at 10.6 cm and 10.5 cm respectively. The estimated length at first capture was lower than the length at maturity inferring that these species do not get the chance to spawn at least once before they are harvested. From the study, it was confirmed that the Carangid stock within Ghana’s coastal waters is currently overexploited and there is a need for a decrease in fishing pressure on carangids to aid in sustainable management of the stocks.