Population statistics of the migratory hilsa shad,Tenualosa ilisha,in Sindh, Pakistan

Abstract

In order to estimate the population dynamics of the hilsa shad, Tenualosa ilisha, fishery in Sindh, the key population parameters of growth, mortalities, recruitment pattern, exploitation and maximum sustainable yield are discussed. Length frequency data were collected from April to October 2004 from the main commercial (hilsa) landings at Thatta, Sindh. Estimated parameters of the von Bertalanffy (Hum. Biol. 10, 181–213) growth model were L∞ = 31.5 cm, K = 1.5 year−1, t0 = −0.10 year as obtained by the electronic length frequency analysis (ELEFAN I). Estimated natural, fishing, and total mortalities were 2.21, 0.673, 2.89 year−1, respectively. The relative biomass per recruit (B′/R) was 0.95 and yield per recruit (Y′/R) was 0.06 using the knife-edge selection. The exploitation ratio at the maximum sustainable yield (MSY) was Emax = 1.0 year−1, fishing mortality at MSY was Fmax = 2.89 year−1, average target Fopt = 0.5 year−1 and Flimit = 1.47 year−1. The catch and effort data from 1981 to 2004 (MFD, Karachi) were analyzed using the catch and effort data analysis (CEDA) computer programme. Estimated biological reference point of MSY for the Fox model was 891 tonnes (t), R2 = 0.75; for the Schaefer and Pella-Tomlinson models MSY = 744 t, R2 = 0.49, the outputs of which appeared to be more conservative than the Fox model which indicated a better fit. The overall situation of hilsa fishery is in severe stress and appears vulnerable to overexploitation. On the basis of the present findings, serious attention is required to provide appropriate access of the fish to the Indus River during the spawning period as well as to impose a ban on fishing during upstream migration and on undersized catch to prevent this traditional fishery in this area.