Sandbar Shark

The sandbar shark (Carcharhinus plumbeus), frequently referred to as the brown shark or thickskin shark, belongs to the family Carcharhinidae, which is native to the Atlantic Ocean and the Indo-Pacific. Distinguished by its notably high first dorsal fin and interdorsal ridge, it should not be confused with the similarly named sand tiger shark (Carcharias taurus).

Recognized as one of the largest coastal sharks globally, the sandbar shark shares close relations with the dusky shark, bignose shark, and bull shark. Its dorsal fin is triangular and exceptionally high, accompanied by elongated pectoral fins. Characterized by robust bodies and rounded snouts shorter than the average shark, its upper teeth exhibit broadly uneven cusps with sharp edges, and its second dorsal and anal fins are of comparable height.

Female sandbar sharks typically reach lengths of 2–2.5 meters (6.6–8.2 feet), while males grow up to 1.8 meters (5.9 feet). The heaviest recorded specimen weighed 240 kilograms (530 pounds). The average fork-length (measured from the tip of the nose to the fork in the tail) is approximately 154.9 cm for females and 151.6 cm for males. Their coloration ranges from bluish-brown to gray or bronze, featuring a white or pale underside. Sandbar sharks may swim solitarily or form sex-segregated groups of varying sizes.

True to its common name, the sandbar shark is frequently found over muddy or sandy bottoms in shallow coastal environments such as bays, estuaries, harbors, or river mouths, although it also inhabits deeper waters (200 m or more) and intertidal zones. Their distribution spans tropical to temperate waters worldwide, with a range in the western Atlantic from Massachusetts to 🇧🇷 Brazil. Juveniles are particularly prevalent in the lower Chesapeake Bay, with nursery grounds extending from Delaware Bay to South Carolina, as well as Bonjuk Bay in Marmaris, Muğla, 🇹🇷 Turkey, and the 🇺🇸 Florida Keys.

Natural predators of the sandbar shark include the tiger shark and, less commonly, the great white shark. In their ecological niche, sandbar sharks are apex predators, preying on fish, rays, crabs, and molluscs. In regions like the Mediterranean or Gulf of Gabés, their diet primarily consists of osteichthyes, octopi, European squid, and cuttlefish.

Discrepancies exist regarding the age at which sandbar sharks reach sexual maturity, though it is generally accepted that females mature around 13 years of age, while males do so at approximately 12 years. These sharks are viviparous, with embryos sustained by a placental yolk sac within the mother. Females demonstrate biennial or triennial reproductive cycles, returning to consistent birthing locations. They ovulate in early summer, giving birth to an average of eight pups after a gestation period of one year. The sandbar shark's typical lifespan ranges from 35 to 41 years.

Despite their substantial size and resemblance to more dangerous sharks such as the bull shark, sandbar sharks are not considered a threat to humans. Documented attacks are exceedingly rare, rendering them one of the safest shark species for aquaria and human interaction. However, on August 2, 2021, an unfortunate incident involved a 12-year-old girl bitten by a sandbar shark in Ocean City, Maryland, requiring 42 stitches.

Current research focuses on the immune system genetics of these sharks, specifically the Major Histocompatibility Complex (MHC) genes, which are pivotal in understanding the adaptive immune system in species like the sandbar shark. Their MHC genes, including class I, class IIα, and class IIβ, share similarities with those of tetrapods rather than typical fish, such as the absence of cysteines in class IIα1 domains and a reduced number of classical loci compared to other animals.