Feeding habits of the scalloped hammerhead shark, Sphyrna lewini, in Mazatlán waters, southern Gulf of California, Mexico

We studied the contents of 556 stomachs of scalloped hammerhead sharks, ranging from 48 to 160 cm TL, caught from off Mazatlán, southern Gulf of California, between October 2000 and April 2005: 449 stomachs had food contents, and 87 prey species were identified. The Index of Relative Importance (IRI) showed that the diet is mainly constituted of dart squids Loliolopsis diomedeae (IRI = 49%) and bony fishes: Carangidae (IRI = 26 %) and Gerreidae (IRI = 7%). According to the values of niche breadth (0.14) and diversity index (3.49), Sphyrna lewini should be a generalist and opportunistic predator, with unselective feeding behaviour: the type and amount of the food consumed are determined by its abundance and availability. The Morisita-Horn indices indicated high niche trophic overlap between sexes (Cλ = 0.95), and low overlap between size classes (Cλ = 0.50).