Sandbar shark

The sandbar shark (Carcharhinus plumbeus), also known as the brown shark or thickskin shark, is a species of requiem shark, and part of the family Carcharhinidae, native to the Atlantic Ocean and the Indo-Pacific. It is distinguishable by its very high first dorsal fin and interdorsal ridge. It is not to be confused with the similarly named sand tiger shark, or Carcharias taurus.

The earliest fossil teeth of this species are known from the Early Miocene of Italy. They appear on the eastern coast of the US around the Middle Miocene, and in Venezuela around the same time. Fossils become more geographically widespread afterwards.

The sandbar shark is one of the largest coastal sharks in the world, and is closely related to the dusky shark, the bignose shark, and the bull shark. Its dorsal fin is triangular and very high, and it has very long pectoral fins. Sandbar sharks usually have heavy-set bodies and rounded snouts that are shorter than the average shark's snout. Its upper teeth have broadly uneven cusps with sharp edges. Its second dorsal fin and anal fin are close to the same height.

Females can grow to 2–2.5 m (6.6–8.2 ft), males up to 1.8 m (5.9 ft). The maximum recorded weight is 240 kg (530 lb). Female sandbar sharks have an average fork-length (tip of the nose to fork in the tail) of 154.9 cm with the males' average fork-length being 151.6 cm. Its body color can vary from a blue-ish brown, grey or bronze, with a white or pale underside. Sandbar sharks swim alone or gather in sex-segregated schools that vary in size.

The sandbar shark, true to its nickname, is commonly found over muddy or sandy bottoms in shallow coastal waters such as bays, estuaries, harbors, or the mouths of rivers, but it also swims in deeper waters (200 m or more) as well as intertidal zones. Sandbar sharks are found in tropical to temperate waters worldwide; in the western Atlantic they range from Massachusetts to Brazil. Juveniles are common to abundant in the lower Chesapeake Bay, and nursery grounds are found from Delaware Bay to South Carolina. Other nursery grounds include Bonjuk Bay in Marmaris, Muğla/Turkey and the Florida Keys.

Natural predators of the sandbar shark include the tiger shark and, rarely, great white sharks.

The sandbar shark itself preys on fish, rays, crabs, and molluscs. They have also been found to primarily consume osteichthyes, or bony fish, octopuses, european squid, and cuttlefish when in areas such as the Mediterranean or the Gulf of Gabés. Sandbar sharks have been described as being a top predator in their ecosystem's food chain.

There are disagreements about when exactly sandbar sharks reach sexual maturity, but most studies conclude that females reach sexual maturity around 13 years of age, while males tend to reach maturity around age 12 years old. Sandbar sharks are viviparous, with the embryos supported in placental yolk sac inside the mother. Females have been found to exhibit both biennial, consistently reproducing every two years and returning to the same place to have deliver the pup, and triennial, reproducing every three years and returning to the same place for delivery, migration and gestation periods. They also ovulate in early summer, and give birth to an average of eight pups, which they carry for 1 year before giving birth. The longevity of the sandbar shark is typically 35–41 years.