Spiny Dogfish (Squalus acanthias)
Alternate common names: Dogfish, Dogshark.
Color: Grey or brown in color, fading to a white belly, with several white spots on sides.
Size: 2 to 3 feet long.
Habitat: Deeper waters near the mouth of the Bay.
Seasonal appearance: May to November.
The spiny dogfish is a small shark with a slender, flattened head, blunt, tapered snout, and a small crescent-shaped mouth. The teeth of the spiny dogfish are small with sharp points that bend outward. The teeth are organized into several rows and are used for grinding, rather than tearing. The first dorsal fin of the spiny dogfish is somewhat larger than the second dorsal fin. Two large, sharp, mildly poisonous dorsal spines are located in front of each dorsal fin. The spiny dogfish uses its spines defensively by curling up its body and striking at an enemy. Spiny dogfish skin is rough and covered by a tooth-like, scaled surface called dermal denticles. The skin feels smooth when rubbed with the grain of the denticles, but feels rough when rubbed against the grain.
Life History and Behavior
Spiny dogfish are the most abundant and most commonly seen of all sharks in Narragansett Bay. There is, however, a similar species of shark found in Rhode Island waters, the smooth dogfish Mustelis canis. Often migrating to find food, the spiny dogfish swims in schools of individuals of similar size. The fish is extremely voracious, often scattering and destroying schools of mackerel and other fish. In addition to eating worms, shrimp, crabs, and comb jellies, the spiny dogfish is one of the major predators of American lobster and large crabs.
Rather than laying eggs or encasing eggs in a capsule like the little skate, spiny dogfish bear live young and can have up to six pups per litter. These fish reproduce slowly, and therefore wild populations are susceptible to over fishing.
Adapted from The Uncommon Guide to Common Life on Narragansett Bay. Save The Bay, 1998.