| Smooth Hammerhead | |
|---|---|
 | |
|
Class |
Fish |
|
Species |
Shark |
The Smooth Hammerhead (Sphyrna zygaena) is a species of hammerhead shark, family Sphyrnidae. A relatively common shark, it is captured, intentionally or otherwise, by many commercial fisheries throughout its range; its fins are extremely valuable for use in shark fin soup. This shark is potentially dangerous and has likely been responsible for a few attacks on humans, though it is less likely to encounter swimmers than other large hammerhead species due to its temperate habitat.
Description[]
The second-largest hammerhead next to the great hammerhead, the smooth hammerhead typically measures 2.5–3.5 m (8.2–11 ft) long, with a maximum recorded length and weight of 5 m (16 ft) and 400 kg (880 lb) respectively. The smooth hammerhead differs from other large hammerheads in the shape of its cephalofoil, which has a curved front margin without an indentation in the center. The cephalofoil is wide but short, measuring 26–29% of the body length across. The nostrils are located near the ends of the cephalofoil, with long grooves running towards the center. There are 26–32 tooth rows in the upper jaw and 25–30 tooth rows in the lower jaw. Each tooth is triangular in shape, with smooth to weakly serrated edges.
The body is streamlined, without a dorsal ridge between the two dorsal fins. The first dorsal fin is moderately tall and falcate (sickle-like) in shape, with a rounded tip. The pectoral and pelvic fins are not falcate, rather having nearly straight rear margins. The anal fin is larger than the second dorsal fin, with long free rear tip and a strong notch in the rear margin. The dermal denticles are densely packed, each with 5–7 horizontal ridges (3 in juveniles) leading to a W-shaped rear margin. The back is dark brownish gray to olive in color, in contrast to the simple brown of most other hammerheads, becoming lighter on the flanks. The belly is white, and sometimes the pectoral fins have dark edges underneath.
Habitat[]
Compared to the scalloped and great hammerheads, the smooth hammerhead stays closer to the surface, in water less than 20 m (66 ft) deep. However, it has been recorded diving to a depth of 200 m (660 ft). It prefers inshore waters such as bays and estuaries, but is sometimes found in the open ocean over the continental shelf, and around oceanic islands. This shark has also been reported entering freshwater habitats, such as the Indian River in Florida. In the summer, smooth hammerheads migrate poleward to stay in cooler water, heading back towards the equator in winter.
Food[]
The smooth hammerhead is an active-swimming predator that feeds on bony fishes, rays, sharks (including of its own species), cephalopods, and to a lesser extent crustaceans such as shrimp, crabs, and barnacles. They readily scavenge from fishing lines. In some areas, stingrays are a favored prey and comprise a majority of its diet. In northern Europe, the smooth hammerhead feeds on herring and seabass, while in North America it takes Spanish mackerel and menhaden. Off South Africa, smooth hammerheads feed on squid such as Loligo vulgaris and small schooling fish such as pilchard over the deep coral reefs at the edge of the continental shelf, with individuals over 2 m (6.6 ft) long taking increasing numbers of smaller sharks and rays. Off Australia, squid are the most important prey, followed by bony fish.