Population biology and assessment of Kawakawa (Euthynnus affinis) in Coastal Waters of the Persian Gulf and Sea of Oman (Hormozgan Province)

Abstract

Length composition data (fork length) of kawakawa(Euthynnus affinis), landed between April 2003 to March 2005 in Coastal Waters of Hormozgan province in Iran ( Persian Gulf and Sea of Oman), were monthly used to estimate the population parameters and for the assessment of the stock. The growth parameters of von Bertalanffy equation were estimated as L � : 87.66 cm, K: 0.51 per year and t 0 : -0.23 year. The estimated value of total mortality, natural mortality and fishing mortality were Z: 2.37, M: 0.65, F: 1.72 per year, respectively. Exploitation ratio (E) and Exploitation rate (U) were estimated as 0.72 and 0.65. The Annual total stock at beginning of year was calculated to be 7924 t and Annual average standing stock (S) was equal to 2994 t. By using analyses knife-edge selection method, biological reference points for kawakawa stock was calculated as, Y'/R (relative yield per recruitment) =0.062, B'/R (relative biomass per recruitment) =0.13, Fmax (Fishing mortality at maximum sustainable yield) =1.6, Emax (Exploitation ratio at maximum sustainable yield) = 0.68; Fopt (Precautionary average target ) =0.33 year -1 and Flimit=0.43 year -1 . As the exploitation ratio of kawakawa stock in this study was calculated to be over 0.5, it strongly recommended minimizing the fishing activity in this area.