DISTINGUISHING FEATURES AND BEHAVIORS

The spiny dogfish is a species of small shark with a slender, flattened head, blunt, tapered snout, and a small crescent-shaped mouth. The teeth of the dogfish are small with sharp points that bend outward. The teeth are organized into several rows and are used for grinding, rather than tearing. Spiny dogfish are most common in the Bay, but the smooth dogfish (Mustelis canis) can also be found.

The 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 dogfish uses its spines defensively by curling up its body and striking at an enemy.

Dogfish skin is rough and covered by a toothlike, 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.

Often migrating to find food, the spiny dogfish swims in schools or packs 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 lobsters and large crabs.

By far, spiny dogfish are the most abundant and most commonly seen of all shark species in the Bay. Rather than laying eggs, this fish bears live young and can have up to six pups per litter.

RELATIONSHIP TO PEOPLE

The spiny dogfish has been increasing in numbers in the North Atlantic, replacing overexploited groundfish stocks such as cod, haddock, and yellowtail flounder. Large numbers of spiny dogfish become entangled in trawls and seine nets, doing tremendous damage to fishing gear. They are also notorious for stealing bait.

Once classified as an underutilized species, commercial fishing of spiny dogfish is at an all-time high. Because they reproduce slowly, more like mammals than fish, wild populations are susceptible to overfishing. In the past they have been used for fertilizer, liver oil, and fish meal, and as a food source sometimes marketed as shark or scallops.