Diet of The milk shark, Rhizoprionondon acutus (Ruppel, 1837) in waters of the Persian Gulf and Oman Sea (Hormozgan province)

The aim of this study was to determine the diet of the milk shark in waters of the Persian Gulf and the Oman Sea in Hormozgan province. Total number of samples collected from the waters of Hormozgan province was 45, of which, 17 and 28 were male and female, respectively. The sex ratio of male to female was 1:1.65 in the studied population, which showed no statistically significant difference between the sex ratio of male and female (X2=2.69, p>0.05). The results of frequency and weight percentage of the stomach contents showed that the highest frequency and weight percentage (47.44 and 63.88%, respectively) were related to teleost fish and then crustaceans (33.33 and 23.30%, respectively). Cephalopods (6.41% and 7.13%, respectively), other prey (8.97% and 3.71%, respectively) and bivalves (3.85% and 1.98%, respectively) were in the next ranks. Results of food preference index showed that the fish food group had a total of 83.72 as the first preferred food of the milk shark. Results of Empty Stomach Index in the milk shark indicated that both males and females and the whole populationin the coasts of Hormozgan province is considered as a gluttonous species. Teleost fish had the highest relative importance of prey (IRI) for both males and females and the whole population of milk sharks, (76.53, 67.73 and 73.71%, respectively). For the population and female sharks, crustaceans and bony fish had the highest Shannon-Wiener biodiversity index with 0.159 and 0.153, respectively, but in male sharks, Shannon-Wiener biodiversity index showed the highest biomass index of bony fish (0.138) compared to crustaceans (0.114). Gastrointestinal index (GSI) in R. acutus shark off the coast of Hormozgan province was 2.62% for males, 2.10% for females and 2.30% for the whole population of this species. The overall results show that a common pattern in the milk shark diet preference is elucidated, in which small bony fish are seen as the most preferred prey, followed by crustaceans.