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

Abstract

Introduction: 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.
Materials & Methods: Total number of samples collected from the waters of Hormozgan
province was45, of which , 17 and 28 were male and female, respectively.
Results: 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 population in 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.
Conclusion: 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.