Mortality and Exploitation of Penaeus monodon in the Andoni River, Nigeria

Abstract

The mortality and exploitation of the giant tiger prawn (P.monodon), an exotic shell fish species whose occurrence in Nigerian coastal waters was first reported in 1999 was investigated in the Andoni River, Nigeria from March 2012 to February, 2013. The stock was determined through data collected from artisanal fishers at Kaa water front on a monthly basis. The weight of each specimen was determined using Ohaus electronic weighing balance while length was measured with vernier caliper. FAO-ICLARM Fish Stock Assessment Tools II (soft ware) was used for data analysis. Population parameters showed that asymptotic length (L?) and growth rate (K) were 31.5cm and 0.870yr?¹ respectively. Natural mortality (M) yr^-1 was equal to 1.64302 while fishing mortality (F) yr^-1 was 0.38698 and total mortality (Z) yr^-1 equalled 2.03. The exploitation rate was 0.1906 while the allowable limit of exploitation (E_max) was equal to 0.421. The present value of exploitation ratio (E = 0.1906) was lower than that associated with the maximum relative yield per recruit (E_max = 0.421). The results indicate that P. monodon was under-fished. Consequently, fishing effort exerted on the stock can be increased by 100-120% of its current value to achieve the maximum yield per recruit.

Key Words: Mortality, Exploitation, Shrimps, Prospect, Niger Delta