Spinner shark

Taxonomy:

Phylum– Chordata

Class– Chondrichthyles

Subclass– Elasmobranchii

Order– Carcharhiniformes

Common Name– Ground Sharks

Family– Carcharhinidae

Common Name– Requiem Sharks

Genus– Carcharhinus

Species– brevipinna

Status: IUCN Red List NEAR THREATENED

Average Size and Length: The Spinner shark has a maximum length of 9.8 feet, but an average length of 6.6 feet.

Average Weight: The average weight is 123 pounds, with a maximum recorded weight of 200 pounds.

Teeth and Jaw: The Spinner shark has forward-pointing furrows at the corners of the mouth. The tooth rows are 15–18 in each half of the upper jaw and 14–17 inches each half of the lower jaw, with two and one small symphysial in the center. The teeth have long, narrow central cusps and are serrated in the upper jaw and smooth in the lower jaw.

Head: The Spinner shark has a long, pointed snout. The eyes are circular and small.

Denticles:  The dermal denticles of the Spinner shark are very closely arranged and overlap, covering the skin completely. The blades are slightly raised and are broader than long. The ridges number usually 7 (on a rare occasion 5), with 7 very short or entirely even teeth. They are in the shape of a diamond.

Demographic, Distribution, Habitat, Environment and Range: In the Western Atlantic Ocean, it can be found 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 can be found 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. Here in Florida, Spinner sharks are migratory and are quite common. They are seen in the bays, and on shore frequenting the surf. Fisherman offshore, as well as land-based fisherman, and surfers come in contact, or witness them spinning out of the water frequently.

The Spinner shark has been reported from the ocean surface to a depth of 330 feet. It prefers water less 98 feet deep, which we do see here in Florida quite often. It does occupy all levels of the water column. It 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 Spinner shark forms schools and is considered a highly migratory species off the Florida and Louisiana coasts and in the Gulf of Mexico, moving inshore during spring and summer months to reproduce and feed.

Diet: A Spinner sharks primary food source is bony fish. They will eat anchovies, sardines, sea catfish, lizardfish, mullets, bluefish, tunas, bonito, croakers, mojarras, jacks and many others. 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 is seized and swallowed whole. Spinner sharks are not equipped with teeth for cutting. 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. The shark’s momentum at the end of these spiraling runs often carries it into the air, giving it its name (this behavior isn’t unique to the Spinner shark, Blacktip sharks do it also, just not as often as Spinner sharks do.

Smaller Spinner sharks may be preyed upon by larger sharks.

Ram-Suction Index: Ram

Aesthetic Identification: The Spinner shark is gray above, sometimes with a bronze sheen, and counter-shaded white below, with a pale white band on the sides. The five pairs of gill slits are long. It has a slim, streamlined body, making it well-engineered for its very unique behavior. 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 somewhat short, narrow, and falcate.

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.

Biology and Reproduction: 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.

The Spinner shark is viviparous. Females give birth to between 3 and 20 (usually 7 to 11) pups every other year, after a gestation period of 11–15 months. Mating occurs from early spring to summer, and parturition in August off North Africa, from April to May off South Africa, and from March to April in the northwestern Atlantic.

Nurseries are inshore beaches or bays with high-salinity water deeper than 16 feet deep. The length at birth is anywhere from 24 inches to 27 inches throughout all locations. It is relative to the location. Spinner sharks are relatively fast-growing sharks: 12 inches per year for newborns, 9.8 inches per year for one-year-olds, 3.9 inches per year for adolescents, and 2 inches per year for adults.

Off South Africa, males mature at 5.9 feet and females at 6.9 feet. In the northwestern Atlantic, males mature at 4.3 feet long and females at 4.9–5.2 feet long, corresponding to ages of 4–5 years and 7–8 years. Spinner sharks generally do not reproduce until they are 12–14 years old. The maximum lifespan has been estimated at 15–20 years or more for a Spinner shark.

Behavioral Traits, Sensing and Intelligence: As mentioned above, Spinner sharks participate in a unique, and aggressive behavior to charge their prey. It is also suggested that Spinner sharks may participate in feeding frenzies; it does form large schools and segregates by sex.

Young sharks prefer cooler water temperatures than adults. Off South Africa, females are found close to shore year-round, while males only appear during the summer.

Speed:  Spinner sharks are very fast, active and energetic swimmers.

Spinner Shark Future and Conservation: According to ISAF (2018), the meat of the Spinner shark is of high quality and sold fresh or dried and salted. In addition, the fins are used for shark fin soup in East Asia, the liver oil is processed for vitamins, and the skin is made into leather products.

Spinner sharks are an important catch of the US commercial shark fisheries operating in the northwestern Atlantic and the Gulf of Mexico. The meat is marketed under the name “Blacktip shark” in the United States, due to that species being considered superior in quality by consumers. It is likely also caught by other fisheries across its range, going unreported owing to confusion with the Blacktip shark. The Spinner shark is also highly regarded by recreational fisherman because of its energetic nature, and leaping out of the water.

Spinner Shark Recorded Attacks on Humans: Spinner sharks do not pose a huge threat to humans. As of 2008, the International Shark Attack File listed 16 unprovoked attacks (including surfers) and one provoked attack attributable to the Spinner shark, none of them fatal.