Fishery status and stock assessment of silver carp (Hypophthalmichthys molitrix) in Mahabad reservoir in fishing season of 1998-1999

Abstract

A total of 150261 kg of different species were caught in Mahabad reservoir of which 101123.5 kg (tantamount to 67.3 % )was silver carp in the fishing season of 1998-1999. From the beginning of the fishing season, fishing effort of only active fishing cooperative were 69 times beach seine haul and for gill net with stretched mesh size of 7 to 15 cm, 2530.7 fishing effort unit (each unit is equal to 100m gillnet for 24 hours). The mean fork length and weight of Silver carp were 51.15±12.07cm and 2429±2272.1g respectively. Exponential Length-Weight relationship for this species was calculated W=0.013 L 3.04 (R2 = 97.64, n=714) which in this equation W is the total weight of fish in g and L is lenght in cm. The Von-Bertalanfy(s) growth parameters (L¥ , K, to) based on length and age data were estimated as: L¥ = 150cm, K = 0.128 per year, to = - 1.141 years). The instantaneous rate of total (Z), Natural (M) and fishing (F) mortality coefficients were 1.68 year-1, 0.22 year-1 and 1.46 year-1 respectively. The exploitation ratio (E) was calculated as 0.82. The biomass of this species was calculated as 158.5 tonnes and according to Gulland(s) formula, the MSY was estimated as 68 tonnes which is less than the catch of this species and decreasing of the fishing effort is recommended.