Latin name

Carcharhinus brevipinna

Other name

Carcharhinus brevipinna

Identification

The spinner shark differs from the blacktip shark in that the first dorsal fin is more triangular and closer to the tail. Adults can also be distinguished by the black edge of the anal fin. Their bodies are densely covered with diamond-shaped placoid scales with 7 (less often 5) small horizontal projections on each scale. Sharks from the Indian and Pacific Oceans tend to be larger than their Northwest Atlantic counterparts. This species has a slender, streamlined body with a distinctive long and pointed snout. Eyes are small and round. There are skin furrows at the corners of the mouth. The number of teeth is 15-18 on each half of the upper jaw and 14-17 on each half of the lower jaw, with 1 or 2 teeth on the symphysis. The teeth end in a long, narrow point; the upper teeth have fine serrations on their margins, while the lower teeth have smooth margins. Five pairs of long gill slits.

Features of fish fins

Dorsal spines (total): 0; Anal spines: 0.

The first dorsal fin is relatively small and usually begins behind the free posterior tip of the pectoral fins. There is no ridge between the first and second dorsal fins. The pectoral fins are rather short, narrow and crescent-shaped. 

Fish colouring

The coloration of the spinner shark is gray, sometimes with a bronze tinge, the belly is white with a sparse white stripe along the sides. Juveniles do not have dark fin edges, while adults have black stripes around the tips of the second dorsal, anal and pectoral fins and the lower lobe of the tail. 

Distribution

There is some uncertainty in the distribution data for the spinner shark due to confusion with the blacktip shark. In the western Atlantic, it is 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 is found from North Africa to Namibia. In the Indian Ocean, it is found from South Africa and Madagascar to the Red Sea and Gulf of Aden, India and nearby islands, Java and Sumatra. In the Pacific Ocean, it occurs off the coasts of Japan, Vietnam, Australia, and possibly the Philippines. Parasitological evidence suggests that these sharks from the Indian Ocean entered the Mediterranean through the Suez Canal and became migratory Lessepsian sharks.

Habitat

The spinner shark can be found at depths of up to 100 m (330 ft) from the surface, although it prefers waters less than 30 m (98 ft) deep and occupies all levels of the water column. This species can be found in coastal waters as well as far offshore, on continental and island shelves. Juveniles are known to enter bays but avoid brackish waters. 

Size

The maximum recorded length of these sharks is 3 m and their mass is 90 kg, while the average size and mass does not exceed 2 m and 56 kg. Spinner sharks grow quite rapidly: newborns grow 30 cm by the age of one, the next year they grow another 25 cm, the annual growth rate for juveniles is 10 cm and for adults - 5 cm. Maximum life expectancy is estimated at 15-20 years or more.

Behavior

The Northwest Atlantic subpopulation of these sharks is known to be migratory. They inhabit warm coastal waters in spring and summer and move south to deeper waters in winter. Fast and active, spinner sharks sometimes form large schools segregated by age and sex. Juveniles prefer cooler water temperatures than adults. Off the coast of South Africa, females remain inshore year-round, while males only appear in summer. Juvenile sharks may be preyed upon by larger conspecifics. 

Food and feeding habits

The diet of these sharks consists mainly of small bony fish, including sardines, herring, anchovies, catfish, mullet, various species of tuna, mackerel, humpback, a variety of perch and flatfish. They also eat rays, cuttlefish, squid and octopus. They often hunt collectively, stalking their prey quickly. Spinner sharks swallow their prey whole, as they lack the teeth to rip it apart. Their hunting tactics are unusual: with their jaws open, they dive vertically through a school of fish to the surface, turn on their axis and grab the prey with their teeth. At the end of the attack, they often jump out of the water due to inertia. Off the coast of Madagascar, these sharks follow schools of migrating mackerel and tuna. They gather around shrimp trawlers and often go into a feeding frenzy.

Reproduction

Spinner sharks are viviparous. Adult females have one functional ovary and two functional uteruses. Each uterus is divided into compartments, one for each embryo. The embryos are initially nourished by the yolk sac. When the embryo reaches a size of about 19 centimeters, the yolk sac empties and forms a placental connection through which the mother provides the embryo with nutrients for the rest of the pregnancy. This species has the smallest ratio of egg size to embryo length in late development among viviparous sharks. There are 3 to 20 pups in a litter. Females give birth every two years, with pregnancies lasting 11-15 months. Sharks mate from early spring to summer. In North Africa, births occur in August, off the coast of South Africa from April to May, and in the Northwest Atlantic from March to April. Pups, 60-77 cm long, are born in coastal areas and estuaries with elevated salinity at depths greater than 5 m. In the Northwest Atlantic, males mature at 1.3 m and females mature at 1.5-1.6 m, corresponding to ages 4-5 and 7-8 years, respectively. Off South Africa, males mature at 1.8 m and females mature at 2.1 m. They usually do not breed before 12-14 years of age. 

Fishing

The meat of this shark species is highly prized and is sold fresh or dried. In addition, in East Asia, the fins are used for soup, the fat is used to make vitamins, and the skin is processed. In the United States, they are a valuable commercial fish, harvested in the Northwest Atlantic and the Gulf of Mexico. They are also highly prized by sport fishermen.

Relationship with a person

These sharks do not usually pose a significant threat to humans, as they do not consider large mammals to be prey, and their small, narrow teeth are adapted for grabbing rather than tearing off pieces. However, they can become agitated in the presence of food and develop feeding fever, so caution should be exercised when hunting underwater with an underwater gun.