Sand Shark. Discusses sand shark; size, colour, habits, diet and breeding. Pictures included, with external links for extra informaiton.

Sand Sharks

The sand shark or 'grey nurse shark' is one of at least four species belonging to the family Odontaspididae. Synonyms include Carcharias taurus, Eugomphodus taurus and Carcharias arenarius. The recognized FAO common name for this species is the sand tiger shark, but it is also known as the grey nurse shark in Australia and the spotted raggedtooth shark in southern African waters.

The large size of the second dorsal fin, and of the anal as well (which is about equal to the first dorsal instead of much smaller) is of itself enough to distinguish this species from all other Gulf of Maine sharks. The fact that the first dorsal fin is located but little in front of the pelvics, and that the trunk seems crowded with fins of equal size, is a useful field mark.

We may also point out that the pectoral fins are not much larger than the other fins-triangular rather than sickle-shaped; that the upper lobe of the tail is nearly one-third as long as head and body together and notched near its tip, with the lower lobe about one-third as long as the upper lobe; and that the head is flat above, the snout short, conical with rather sharp tip.

The teeth also (alike in the two jaws) are diagnostic, being long, narrow, sharp-pointed, and smooth-edged, with one (rarely two) small spurs ('denticles') on either side near the base.

Size

Most of the sand sharks that are caught in the northern part of their American range, from Delaware Bay to Cape Cod, are immature, of perhaps four to six feet. But adults up to eight or nine feet long are reported there from time to time, especially from the vicinity of Nantucket, where a commercial shark fishery yielded many of them in the early 1920's. And large ones, alone, have been reported from North Carolina, southward. The greatest recorded length is 10 feet five inches, from south-western Florida. And the sand shark does not mature sexually until perhaps seven feet long, or more. A weight of 250 pounds is recorded for one eight feet 10 inches long, showing how much lighter a fish this is, length for length, than various other sharks.

Colour

Light grey-brown above, darkest along back, snout, and upper sides of pectorals, paling on the sides to greyish white on lower surface; sides of trunk rearward from pectorals variously marked with roundish to oval spots, of which there may be upwards of 100, varying in colour from yellowish brown to ochre yellow. The rear margins of the fins are edged with black on some specimens, but not on others.

Habits and Food

Despite its trim appearance and voracious appetite, this is a comparatively sluggish shark, living mostly on bottom or close to it; more active and taking a bait more freely at night than by day. During its summer visits to the New England coast it holds so close to the coast that it has never been reported from Georges Bank, or from the outer part of the Continental Shelf. Most of those caught are from depths not greater than one to five fathoms, occasionally perhaps as deep as 10 fathoms, and many come right in to tide line along the beaches. They may sometimes be seen moving slowly to and fro at the surface, over bars, with dorsal and caudal fins showing above the water; and they sometimes enter the mouths of rivers.

They capture great numbers of small fish, which are their chief diet, particularly menhaden, cunners, mackerel, skates, silver hake, flounders, alewives, butterfish, and south of Cape Cod, scup, weakfish, and bonito. Sand sharks have been seen surrounding and harrying schools of bluefish; they have even been known to attack nets full of bluefish, which gives a measure of their voracity. They also eat lobsters, crabs, and squid.

Breeding

The eggs of the sand shark are hatched within the parent and are retained there until the resultant young are ready for independent existence, but there is no placental connection between mother and developing embryo. It has recently been discovered that while a ripe female contains a large number of eggs, only two embryos develop as a rule, one in each oviduct; they are nourished (at least largely) by swallowing the unfertilised eggs with which the stomach of the embryo becomes greatly distended.

External Links:
Beach-Net: The Sand Shark
The Sand Shark