Population assessment and yield per recruit of longtail tuna (Thunnus tonggol) in Northern of the Persian Gulf and Oman Sea (Iran, Hormozgan Province)

The purpose of this paper was to detail some important biological aspects of T. tonggol in coastal waters of Hormuzgan Province(Persian Gulf and Oman Sea). A total monthly data of 4383 individuals ranging from 25 to 124 cm fork length were collected from April 2015 to March 2016. The data were analyzed with FiSAT II software using the ELEFAN1  package  to estimate the  population parameters. The length-weight relationship was:  TW=0.00002FL2.87(R2=0.97)and showed isometric growth for T. tonggol. Growth parameters were computed L∞=129.6 cm, K=0.39 year-1 and t0=−0.28 with the growth performance index, φ’ of 8.7. The total mortality(Z) estimated 1.58 year-1 using catch curve method. The natural(M) and fishing(Fcurr) mortality were obtained 0.49 year-1 and 1.09 year-1 respectively. The exploitation ratio was 0.69. Length at first capture (Lc) was estimated as 60.2 cm fork length.    The yield per recruit (Y/R) maximized in maximum fishing mortality rate 0.85 year-1. The biomass per recruit decrease to 17.2% of unexploited biomass(Virgin biomass) at Fcurr  The current fishing mortality exceed optimum fishing mortality(Fopt)and limit fishing mortality(Flimit)biological reference points. The results indicated that population of T. tonggol is overexploited in the Persian Gulf and Oman Sea and no scope for improving production of this species.