The spinner shark (carcharhinus brevipinna) is one of 400 known species of sharks. It has a large and slender build with a long and pointed snout. An adult male can reach 9.8 feet (298.704 cm) and weigh 198 pounds (89.811 kg). Both males and females mature between 5.2-6.7 feet (1.58-2.04 m) then continue to grow approximately two inches (5.08 cm) a year until they peak at about age 20.
Spinner sharks congregate in large schools migrating in warm waters in the Gulf of Mexico off the Florida and Louisiana coast, in the northwestern Atlantic, the southern Mediterranean, the Indian Ocean and western central Pacific, including Australia.
While feeding, the spinner shark uses a leaping and spinning technique to catch fish as they break the surface of the water while passing through a school of swarm fish. This is how the shark got its name. Their preference is a wide variety of small fish such as anchovies, herrings and sardines. They feed on larger sea catfish, tunas, bonito, cuttlefish, squid and octopi. They are known to eat small sharks and rays, which are a close relative as well.
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As with all sharks that inhabit the open ocean, their countershadings camouflage them from predators. These color patterns shade the upper portion with dark gray or bronze coloring to make it difficult to differentiate them against the dark ocean water. Their light underbellies blend with the surface water when viewed from below. The spinner shark is distinguished from the blacktip shark by a striking black tip on the anal fin of adults.
The spinner shark has excellent eyesight and hearing. Their vision is actually ten times more sensitive to light than humans are. However, the structure of their small, round eyes suggests to researchers that they may be far-sighted. Sharks were once considered to have poor vision but we now know they actually have exceptional vision. Eyesight varies in sharks depending on specie, size and focusing ability.
The spinner shark’s ears are inside their head. They have excellent hearing and their best range of frequencies is below 1,000 hertz, which is normal for most natural aquatic sounds.
Spinner sharks are requiem sharks in that they are live bearing, migratory sharks. They deliver 3 to 15 “pups” in the inshore nursery grounds after a gestation period of 12-15 months. The pups are 1.97 to 2.46 ft (60 to 75 cm) at birth and grow approximately 8 inches (20 cm) during the first six months of life. They continue in the warm coastal waters for the first years of their life. After giving birth the female has completed her role, has little to do with the offspring, and has even been known to eat them.
The spinner shark is not aggressive when it comes to human contact and will not attack unless provoked. Its numerous, small, sharp teeth are not designed for attacking large prey. During their lifetime, they can shed thousands of teeth as one breaks off, a new one can immediately replace it.
Humans who eat fish find fresh spinner shark as an exceptional dish. It is also eaten dried, salted and smoked. Vitamin oil is produced, using their livers.
All sharks have an exceptional immune system and two extra organs. It is still unclear exactly why they developed them or specifically what they do. We do know they have broad-spectrum antibodies, which allows for an excellent disease resistant system. Unfortunately, it has not been scientifically verified that this translates to using the shark for medicinal purposes, such as shark cartilage.
However, research continues to be promoted that may expose sharks to hold some of our greatest medical answers. It has often been suggested that one of our greatest enemies of the sea may one day become one of our most trusted saviors.