Spinner Shark

The spinner shark, scientifically known as Carcharhinus brevipinna, is a notable member of the Carcharhinidae family, renowned for its unique feeding behavior that involves spinning leaps. This species predominantly inhabits tropical and warm temperate waters globally, with the exception of the eastern 🌊 Pacific Ocean. It typically resides in both coastal and offshore environments up to depths of 100 meters (330 feet), although it shows a preference for shallower waters.

Resembling a larger form of the blacktip shark (C. limbatus), the spinner shark features a slender physique, an elongated snout, and distinct black-marked fins. Key distinguishing features from the blacktip shark include the placement and shape of the first dorsal fin and the presence of a black tip on the anal fin in adults. The species grows to a maximum length of approximately 3 meters (9.8 feet).

Spinner sharks are agile and sociable hunters, primarily preying on small bony fishes and cephalopods. When targeting schools of fish, they demonstrate a feeding mechanism by swiftly ascending through the school while spinning, which culminates in an aerial leap. This species is viviparous, with females yielding litters ranging from three to 20 offspring biennially. The juveniles are birthed in coastal nursery zones and exhibit relatively rapid growth. Although generally not hazardous to humans, spinner sharks may display aggressive behavior when stimulated by food. They are commercially valuable for their meat, fins, liver oil, and skin, and are prized in recreational fishing for their vigorous fight. The International Union for Conservation of Nature (IUCN) has classified the spinner shark as Vulnerable globally.

Distribution and Habitat

The spinner shark's geographical distribution extends across various regions, although some data discrepancies exist due to potential misidentification with blacktip sharks. In the Western Atlantic, it is found from North Carolina to the northern 🌊 Gulf of Mexico and includes areas such as the 🇧🇸 Bahamas and Cuba, extending down to southern 🇧🇷 Brazil and Argentina. Within the Eastern Atlantic, it ranges from the coast of North Africa to Namibia. In the 🌊 Indian Ocean, its presence spans from 🇿🇦 South Africa and 🇲🇬 Madagascar through the 🌊 Red Sea and the 🌊 Gulf of Aden, up to 🇮🇳 India, Java, and Sumatra (🇮🇩 Indonesia). In the 🌊 Pacific Ocean, sightings have been reported off 🇯🇵 Japan, Vietnam, 🇦🇺 Australia, and possibly the 🇵🇭 Philippines. Parasitological indicators suggest that 🌊 Indian Ocean spinner sharks might have migrated via the Suez Canal (🇪🇬 Egypt) into the Mediterranean Sea.

Spinner sharks have been recorded at ocean depths up to 100 meters (330 feet), though they usually prefer depths less than 30 meters (98 feet) and occupy the entire water column. Their habitats span from coastal waters to offshore areas encompassing continental and insular shelves. While juveniles sometimes venture into bays, they tend to avoid brackish environments. The northwest Atlantic subpopulation demonstrates migratory behavior, residing in warmer inshore waters during spring and summer, then moving southward into deeper waters for the winter.

Physical Characteristics and Behavior

On average, a spinner shark measures 2 meters (6.6 feet) in length and weighs approximately 56 kilograms (123 pounds), with the possibility of reaching a size of 3 meters (9.8 feet) and 90 kilograms (200 pounds). Specimens from the Indo-Pacific region are generally larger than those from the northwest Atlantic. The body is lean and aerodynamic, characterized by a long, pointed snout and small, circular eyes. The mouth's corners sport forward-pointing furrows. The dentition consists of 15–18 tooth rows per half of the upper jaw and 14–17 in the lower jaw, complemented by two small central teeth. These teeth feature long, narrow central cusps with fine serrations in the upper jaw and are smooth in the lower jaw. Five pairs of elongated gill slits are present.

Morphology

The first dorsal fin is relatively small, generally originating behind the pectoral fins' rear tips, with no ridge connecting the first and second dorsal fins. The pectoral fins are moderately short, narrow, and falcate in shape. The skin is densely clad with diamond-shaped dermal denticles that have seven (or seldomly five) shallow horizontal ridges. The dorsal coloration is gray, occasionally with a bronze sheen, contrasting with the white ventral side and a subtle white lateral band. While younger sharks exhibit unmarked fins, larger individuals have black-tipped fins.

Behavior and Parasitology

Spinner sharks are fast, active swimmers and can form large, age- and sex-segregated schools. Off the coast of 🇿🇦 South Africa, females remain nearshore year-round, whereas males are predominantly present in the summertime. Smaller spinner sharks may fall prey to larger sharks, and they host several parasitic species, including Kroyeria deetsi, Nemesis pilosus, and Nemesis atlantica on the gills; Alebion carchariae on the skin; Nesippus orientalis in the mouth and gill arches; and Perissopus dentatus in the nares and fin margins.

Feeding Habits

The spinner shark's diet consists mainly of small bony fish such as tenpounders, sardines, herrings, and anchovies, as well as sea catfish, lizardfish, mullets, and others. The species also consumes stingrays, cuttlefish, squid, and octopus. These sharks are often observed chasing schools of prey at high speeds, capturing and swallowing individual prey whole due to their lack of cutting dentition. An unusual feeding method is employed when hunting schooling fish, where the shark charges upward while spiraling, often resulting in airborne leaps. This distinctive behavior contributes to their common name and distinguishes them from blacktip sharks, which engage in similar actions less frequently. Spinner sharks in 🇲🇬 Madagascar follow migrating fish schools and gather around shrimp trawlers to consume discarded bycatch.

Reproductive Biology

Spinner sharks are viviparous, with females having a single functioning ovary and dual functioning uteri, each divided into compartments for embryos. Initially sustained by a yolk sac, the embryos develop a placental connection upon exhausting the yolk supply, facilitating maternal nutrient provision. This species possesses the smallest ova in comparison to its fully mature embryos among viviparous sharks. Females deliver litters of three to 20 (typically seven to 11) pups biennially, following an 11–15 month gestation. Mating occurs from spring to summer, with births taking place in August off North Africa, April-May off 🇿🇦 South Africa, and March-April in the northwestern Atlantic. Pup delivery occurs in nursery areas characterized by bays, beaches, and high-salinity estuaries, generally deeper than 5 meters (16 feet). The species can live up to 15–20 years or longer.

Human Interaction and Conservation

Spinner sharks typically do not pose substantial threats to humans, as they do not recognize large mammals as prey given their grasp-oriented teeth. However, they may become agitated when food is present, necessitating caution during spearfishing encounters. As of 2008, the International Shark Attack File recorded 16 unprovoked and one provoked non-fatal attacks attributed to spinner sharks.

The species' meat is valued for its quality, available fresh or processed, with the fins being utilized in East Asian shark fin soup, liver oil for vitamins, and skin for leather products. In the 🇺🇸 United States, spinner sharks are commonly marketed as "blacktip shark" due to consumer preferences, despite frequent unreported catches in fisheries across their range. Recreational anglers prize the spinner shark for its spirited fight and frequent aerial displays.

The IUCN¹ lists the spinner shark as Vulnerable globally, largely due to its frequent use of coastal habitats, which increases susceptibility to human exploitation and habitat degradation. The spinner shark fishery in the northwest Atlantic is regulated under the 1999 Fishery Management Plan by the US National Marine Fisheries Service, categorizing it as a "large coastal shark" for commercial quotas and recreational bag limits.