Growth modelling of milk shark, Rhizoprionondon acutus (Ruppel, 1837) from waters of the Persian Gulf and Oman Sea (Hormozgan province)

This study aimed to investigate Growth modelling of the milk shark (Rhizoprionondon acutus Ruppel, 1837) from October 2019 until march 2021 for 18 months in northern waters of the Persian Gulf and the Oman Sea (Hormozgan Province). Overall, 317 shark samples of R. acutus including 137 males and 180 females were weighted. Results of the present work indicated that length-frequency distribution of both sexes were statistically different. Exponential relationship between total length and total weight of males and females were as W=0.0021L3.1508 and W=0.003L3.062 , respectively. After optimization by a non-linear regression through least square method, this relationship was obtained for males and females as W=0.0028L3.078 and W=0.0025L3.106, respectively. Males were estimated for the oldest age at 8 years with the length of 91.15 cm while females were estimated for the oldest age and tallest length at 10 years and 95.5 cm, respectively. By adoption of multi-modelling approach, the best model fittedd to indicate how to grow for the females of milk shark was Gampertz Growth Model (AIC=48.14, ∆AIC = 0). Logistic model had also a considerable protection to draw the growth of females according to AIC (AIC=50.02, ∆AIC= 1.87).  The best model fitted to show how to grow the males of milk shark was Logistic Model (AIC=36.33, ∆AIC= 0). Gampertz model had also a moderate protection to draw the growth of males (AIC=42.46, ∆AIC= 6.12), but three parameterized Von Bertalanfy model showed no efficneby to draw the gorowth of males (AIC= 53.2, ∆AIC= 16.86). . This study was performed for the first time on growth and mortality parameters of the milk shark in Iranian waters of the Persian Gulf and Oman Sea. Regarding the legal and illegal fishing pressure of this valuable species, this is recommended to apply the presented results for wider future studies as a basic study and to monitor its stock status with more precision annually, so as the managers can use these results to adopt scientific-management approaches for the protection of this precious species from extinction.