One of the most abundant sharks globally, Pacific spiny dogfish belongs to the family Squalidae (the dogfish family). Pacific spiny dogfish range from the Bering Sea to Baja California to Japan and the Korean Peninsula. They are most common off the west coast of the U.S. and British Columbia. Dogfish are typically bottom dwellers and inhabit depths from shallow coastal waters to 4,055 ft. (1,236 m). They prefer water temperatures ranging from 44.6° F to 59° F (7-15° C).
Pacific spiny dogfish are small, streamlined sharks. Males can grow to 3.3 ft. (1 m), while females measure a maximum length of 4 ft. (1.2 m). A dogfish has a distinctive snout, large eyes, and a flattened head. The body has a cylindrical shape. The top half is dark gray with scattered white spots, and this color fades to light gray or white on the underneath side of the fish. The teeth of a dogfish have sharp edges, but they are specialized for grinding instead of tearing. Dermal denticles comprise the scales of a dogfish. These denticles are the same rigid material found in their teeth, and they make the skin very tough.
A dogfish does not have an anal fin, but it has two dorsal fins, with a spine in front of each fin. These spines are venomous, and the shark uses them as protection against potential predators, such as other sharks or humans. The dogfish employs its two dorsal fins in different ways. The first dorsal fin helps it maintain stability while swimming, and the second dorsal fin provides thrust. The large caudal fin (or tail) allows the shark to maneuver quickly and efficiently through the water.
A dogfish has five gills on either side of its body, but unlike bony fish, a dogfish does not have gill covers. To breathe through these gills, the shark must remain in constant motion, so it either must continually swim or rest in a current where water rushes past its gills. A dogfish has an adaptation called spiracles, aiding it to breathe in calm water. These specialized gills, located behind the eyes, allow the shark to breathe when resting or eating.
Dogfish earned their common name from fishermen who observed them hunting in packs like dogs. Schools of hundreds of dogfish swim close together during the day, hunting herring, capelin, other small fish, squid, octopus, and even jellyfish. The dogfish uses its teeth and not its spines when feeding. It uses its spines for protection. Scientists think dogfish eat less in the winter when they migrate to great depths. They are preyed upon by larger sharks, seals, orcas, and some larger fish.
Spiny dogfish can live 100 years, and females do not reach sexual maturity until they are approximately 35 years old. Males can reproduce at an average age of 19. Males internally fertilize females in October or November. Dogfish are ovoviviparous, meaning females give birth to live young, and they have a gestation of nearly 24 months, the longest of any vertebrate. They give birth to up to 22 pups, and the newborns range in length from 8 ½ to 12 inches (21.6 – 30.5 cm).
Pacific spiny dogfish stocks remain stable and are carefully managed. In some areas of the world, a commercial market exists for dogfish, and they are considered a good food fish, but they are not yet in demand as a food source in the United States.
We usually catch a few dogfish each year during our sportfishing trips, but this past summer, we landed as many as 20 per day while halibut fishing. Dogfish are tricky to release because while you try to get the hook out of its mouth, the shark attempts to whip its body into a position to stab you with one of its venomous spines. I was not pleased to encounter so many dogfish this past summer, but more importantly, I wondered why we were catching so many dogfish. I speculate that the dramatic decrease in the Pacific cod population led to an increase in small fish species typically eaten by cod. Dogfish probably are exploiting an opening in the food chain. Will their presence affect the abundance of other fish species in this region of the North Pacific? Only time will tell.
Happy holidays, and I wish us all a nicer, brighter 2021!
Robin Barefield is the author of four Alaska wilderness mystery novels, Big Game, Murder Over Kodiak, and The Fisherman’s Daughter, and Karluk Bones. Also, sign up below to subscribe to her free, monthly newsletter on true murder and mystery in Alaska, and listen to her podcast, Murder and Mystery in the Last Frontier.
