Spinner Shark

The average spinner shark is 2 m (6.6 ft) long and weighs 56 kg (123 lb); this species attains a maximum known length and weight of 3 m (9.8 ft) and 90 kg (200 lb). Indo-Pacific sharks are generally larger than those from the northwest Atlantic. This species has a slim, streamlined body with a distinctive, long, pointed snout. The eyes are small and circular. Prominent, forward-pointing furrows occur at the corners of the mouth. The tooth rows number 15–18 in each half of the upper jaw and 14–17 in each half of the lower jaw, with two and one tiny symphysial (central) teeth, respectively. The teeth have long, narrow central cusps and are finely serrated in the upper jaw and smooth in the lower jaw. The five pairs of gill slits are long. The first dorsal fin is relatively small and usually originates behind the free rear tip of the pectoral fins. No ridge exists between the first and second dorsal fins. The pectoral fins are moderately short, narrow, and falcate (sickle-shaped). The body is densely covered with diamond-shaped dermal denticles with seven (rarely five) shallow horizontal ridges. The coloration is gray above, sometimes with a bronze sheen, and white below, with a faint white band on the sides. …

Some uncertainty exists in the distribution data for the spinner shark due to confusion with the blacktip shark. In the Western Atlantic Ocean, it occurs from North Carolina to the northern Gulf of Mexico, including the Bahamas and Cuba, and from southern Brazil to Argentina. In the Eastern Atlantic, it occurs from off North Africa to Namibia. In the Indian Ocean, it is found from South Africa and Madagascar, to the Red Sea and the Gulf of Aden, to India and nearby islands, to Java and Sumatra. In the Pacific Ocean, it occurs off Japan, Vietnam, Australia, and possibly the Philippines. Parasitological evidence suggests that Indian Ocean spinner sharks have passed through the Suez Canal into the Mediterranean Sea, becoming Lessepsian migrants. The spinner shark has been reported from the ocean surface to a depth of 100 m (330 ft), though it prefers water less than 30 m (98 ft) deep, and occupies all levels of the water column. This species may be found from coastal waters to well offshore, over continental and insular shelves. Juveniles have been known to enter bays, but avoid brackish conditions. The northwest Atlantic subpopulation is known to be migratory; in spring and summer, they are found in warm inshore waters, and in winter, they move south into deeper water.

The spinner shark is a fast, active swimmer that sometimes forms large schools, segregated by age and sex. Young individuals prefer cooler water temperatures than adults. Off South Africa, females are found close to shore year-round, while males only appear during the summer. Smaller spinner sharks may be preyed upon by larger sharks. Known parasites of the spinner shark include the copepods Kroyeria deetsi, Nemesis pilosus, and N. atlantica, which infest the shark's gills, Alebion carchariae, which infests the skin, Nesippus orientalis, which infests the mouth and gill arches, and Perissopus dentatus, which infests the nares and the rear margins of the fins.

Feeding. Spinner sharks feed primarily on small bony fish, including tenpounders, sardines, herring, anchovies, sea catfish, lizardfish, mullets, bluefish, tunas, bonito, croakers, jacks, mojarras, grunts, and tongue-soles. They have also been known to eat stingrays, cuttlefish, squid, and octopus. Groups of spinner sharks are often found pursuing schools of prey at high speed. Individual prey are seized and swallowed whole, as this shark lacks cutting dentition. This species employs an unusual tactic when feeding on schools of small fish; the shark charges vertically through the school, spinning on its axis with its mouth open and snapping all around it. …