M. Darvishi - Gorgan University of Agricultural Sciences and Natural Resources.
S.Y. Paighambari - Gorgan University of Agricultural Sciences and Natural Resources.
A.R. Ghorbani - Gorgan University of Agricultural Sciences and Natural Resources.
F. Kaymaram - Iranian Fisheries Science Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran

The purpose of this study was to find some important biological aspects of Thunnus tonggol in coastal waters of Hormozgan Province (Persian Gulf and Oman Sea). A total monthly data of ۴۳۸۳ individuals ranging from ۲۵ to ۱۲۴ cm fork length were collected from April ۲۰۱۵ to March ۲۰۱۶. The data were analyzed with FiSAT II software using the ELEFAN۱ package to estimate the population parameters. The length-weight relationship was TW=۰.۰۰۰۰۲ FL۲.۸۷ (R۲=۰.۹۷) showing an isometric growth for T. tonggol. Growth parameters were computed as L∞=۱۲۹.۶ cm, K=۰.۳۹ year-۱ and t۰=−۰.۲۸ with the growth performance index, φ’ of ۸.۷. The total mortality (Z) was estimated ۱.۵۸ year-۱ using catch curve method. The natural (M) and fishing mortality (Fcurr) were obtained ۰.۴۹ and ۱.۰۹ year-۱, respectively. The exploitation ratio was ۰.۶۹. Length at first capture (Lc) was estimated as ۶۰.۲ cm fork length. The yield per recruit (Y/R) maximized in maximum fishing mortality rate ۰.۸۵ year-۱. The biomass per recruit decreased to ۱۷.۲% of unexploited biomass (virgin biomass) at Fcurr. The current fishing mortality exceeds optimum fishing mortality (Fopt) and limit fishing mortality (Flimit) as biological reference points. The results indicated that population of T. tonggol is overexploited in the Persian Gulf and Oman Sea and there no further scope for improving the exploitation of this species.

Thunnus tonggol, Longtail tuna, Population dynamics, Persian Gulf, Oman Sea