Spinner Shark
The Spinner Shark is a species of requiem shark, family Carcharhinidae, named for the spinning leaps it makes as a part of its feeding strategy. This species is not usually dangerous to humans but may become belligerent when excited by food. Spinner sharks are valued by commercial fisheries across their range for their meat, fins, liver oil, and skin. They are also esteemed as strong fighters by recreational fishers. The International Union for Conservation of Nature (IUCN) has assessed this species as Near Threatened worldwide and Vulnerable off the southeastern United States.
Description[]
The average spinner shark is 2 m (6.4 ft) long and weighs 56 kg (123 lbs); this species attains a maximum known length and weight of 3 m (10 ft) and 90 kg (198 lbs). 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. There are prominent forward-pointing furrows 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 2 and 1 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. There is no ridge 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 7 (rarely 5) shallow horizontal ridges. The coloration is gray above, sometimes with a bronze sheen, and white below, with a faint white band on the sides. Young individuals have unmarked fins; the tips of the second dorsal fin, pectoral fins, anal fin, and lower caudal fin lobe (and sometimes the other fins as well) are black in larger individuals. The spinner shark differs from the blacktip shark in that its first dorsal fin is slightly more triangular in shape and is placed further back on the body. Adults can also be distinguished by the black tip on the anal fin.
Habitat[]
The spinner shark has been reported from ocean surface to a depth of 100 m (330 ft), though it prefers shallow water less than 30 m (100 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.
Food[]
Spinner sharks feed primarily on small bony fishes, including tenpounders, sardines, herring, anchovies, sea catfish, lizardfish, mullets, bluefish, tunas, bonito, croakers, jacks, mojarras, and tongue-soles. They have also been known to eat stingrays, cuttlefish, squid, and octopus.