Spiny Dogfish (Squalus acanthias)

KINGDOM Animalia
PHYLUM Chordata
CLASS Chondrichthyes
ORDER Squaliformes
FAMILY Squalidae

This small shark (up to 130 cm) is a slender fish with two prominent dorsal fins, each with a spine at its front. These spines can inflict a toxic wound. Pectoral and pelvic fins are also conspicuous, but there is no anal fin. The caudal fin has an enlarged upper lobe, as in most sharks, very effective at propelling the shark through the water rapidly. There are scattered small white spots on its gray body.

Shark scales are very different from those of bony fishes. They are made of the same material as shark teeth and are often called dermal denticles (literally, teeth of the skin). Thus sharks have rough skin, rather like sandpaper. Hard as granite and strong as steel, these scales are like a suit of chain mail; no wonder sharks have been around over 400 million years, already diverse long before the dinosaurs appeared. The scales increase in number as a shark grows, rather than increasing in size as in a bony fish.

Like other sharks, Spiny Dogfish have a varied diet, but much of their food in Puget Sound consists of small schooling fish such as herring and sandlance. When feeding on the bottom, they take many crustaceans. They are eaten by larger sharks and marine mammals. Amazingly, giant Pacific octopus are able to capture dogfish that venture near their lairs.

Unlikely to be seen in the water, Spiny Dogfish are often pulled up by fishermen trying for more edible species. They are abundant in Puget Sound and, in fact, all over the world in cold waters at north temperate latitudes. They move into shallow coastal waters for the summer, migrating back into deeper waters (up to 1200 m) for the winter.

These sharks are often in large schools and have been a staple of some fisheries for years, but they have been overharvested in many areas. They grow very slowly and may live up to 100 years, surprisingly long for a relatively small animal. Females mature at 23 years and give birth to 1-20 live young after a gestation period of 18-24 months, the longest known for any shark or ray. Thus they can breed only every other year. Although not a favored fish in the northeast Pacific, there are catch limits for commercial fisheries.