Growth parameters and mortality rates of giant river-catfish <i>Sperata seenghala </i> from the Indus river, Pakistan

Abstract

1462-1469Length frequency of Sperata seenghala1 from the Indus River were collected during the months of February, March, April, May and June in 2011. The sample consisted of n= 133 pairs of length and weight data. The length ranged from 46 to 113 cm TL (65.661±15.995 cm), while the weight varied from 500 to 7500 g TW (1806.391±1481.456 g). Length-weight relationship was calculated as a= 0.04, b= 3.047 (R2= 0.99). The von Bertalanffy growth function parameters for S. seenghala were L∞= 117.60 (TL cm) and K= 0.370 year-1, while the age at zero length was t0= -0.513 year. The total instantaneous mortality rate (Z) was estimated at 95% CI of 0.77-1.22 (Z= 1.00 year-1) in the Indus River. The natural mortality (M) was computed as M= 0.556 year-1 at an average annual temperature of surface water of 21oC, whereas the fishing mortality was estimated as F= 0.444 year-1. Therefore, exploitation ratio (E= F/Z) was calculated as E= 0.444. The growth performances indices for L∞ and W∞ were computed Φ'= 3.709 and Φ= 2.175 respectively. When tc was at 1, the yield per recruit analysis found that Fmax was at 0.85 year-1 and F0.1 at 0.75 year-1. The current age at first capture was about 1 year, the Fcurrent rate was 0.444 year-1. Thus the current fishing mortality rate was smaller than Fopt= 0.556 year-1, Fmax= 0.85 year-1 and F0.1= 0.75 year-1. Therefore, we can assume that the current stock of this important fishery resource is not over-fished

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