Background

Sandbar shark ( Carcharhinus plumbeus). National Aquarium in Baltimore.

The sandbar shark belongs to the family of requiem sharks, or Carcharhinidae, which contains more than 80 species. Seven species occur in Chesapeake Bay waters.

All requiem sharks are voracious predators of finfish, rays, bottom-dwelling animals, seabirds, or turtles, and they will swim alone or gather in gender-segregated schools of varying size. They tend to be most active at night, dawn and dusk. Requiem shark development can be either ovoviparous (in which the embryo develops within the protection of the mother's body and receives continuous nourishment from the yolk store) or viviparous (in which the young receives nourishment from a placenta and other maternal tissues, and the process results in the birth of live young).

Habitat and Life Cycle

The sandbar shark, Carcharhinus plumbeus, 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 meters or more) as well as the intertidal zones. Sandbar sharks are found in tropical to temperate waters worldwide, but in the western Atlantic they range from Massachusetts to Brazil and visit the Chesapeake Bay seasonally, from early spring to fall. Juveniles are common to abundant in the lower Bay, which is probably one of the most important nursery grounds on the East Coast for this species.

The sandbar shark is also known as the "thickskin shark," and is considered large for a coastal shark. Its close relatives include the dusky shark, big nose shark and bull shark. It has a very high, nearly triangular first dorsal fin, whose height is as much as 18 percent of the shark's total length. This species tends to have a stout body, with a rounded, short snout. Its upper teeth have broadly serrated cusps with finely serrated edges. The sandbar shark's second dorsal fin and anal fin are about the same height. Its body is a bluish or brownish gray, sometimes bronze, with a pale or white underside. Adult females grow to a maximum length of 7 to 8 feet, and males reach 6 feet.

• Sandbar sharks are bottom feeders and prey heavily on blue crabs in the Bay. They also consume fresh fish such as sardines, shad, menhaden, eels, barracuda, mackerel, grouper, croaker, flounder, skates, stingrays, squid, shrimp, mollusks, and smaller sharks.
• This species has few predators other than humans. Shark pups are sometimes preyed upon by tiger sharks and adults by great whites. Although they can be found near recreational swimming areas, they are not known to attack humans.
• Reproduction in this species is viviparous. Embryos are supported by a placental yolk sac inside the mother. Females reproduce once every two years, and give birth to 8-10 live young after a 12-month gestation period.
• Sandbar sharks reach maturity between 3 and 13 years, and their life spans rarely exceed 21 years. Since they reproduce only once in two years, populations are vulnerable to being overfished. Since the 1940s, this has been an important commercial shark species, and fisheries increasingly pose a threat to populations in the lower Bay. The species constitutes about half of the commercial shark catch on the East Coast of the U.S.
• Animals are harvested for their meat (for human consumption), hides, fins (for human consumption), and livers, which are valued for their vitamin-rich oil.
• Sandbar sharks are commonly caught using long lines, but are also harvested with gill nets and by anglers using rod and reel.

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Last modified: 8/17/05