Tag Archives: Dogfish Shark

Pacific Spiny Dogfish Shark (Squalus suckleyi)

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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.

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Sharks in Alaska

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Our guests are often surprised to learn sharks feed and swim in the frigid North Pacific. We catch spiny dogfish sharks when halibut fishing, and large salmon sharks terrorize commercial salmon gillnetters by ripping enormous holes in their nets when stealing fish from the mesh. Pacific sleeper sharks also live in Alaska’s waters, but sleeper sharks remain elusive, and biologists do not know much about their biology, diet, and habits. These three species fascinate me, and I think you will enjoy learning about their longevity, reproductive biology, and the mechanisms each species employs to stay warm in the frigid waters surrounding Alaska. I will cover each shark in detail in future posts, but for now, let me give you an overview of sharks in Alaska.

The three shark species I listed above are the most common but not the only sharks trolling the North Pacific. Over the past several years, ocean waters in the region have warmed, encouraging other shark species to venture into these nutrient-rich areas. Great white sharks began exploring Alaska in the 1970s, but recent, more frequent sightings suggest an increasing number of great whites have discovered the North Pacific’s fertile feeding grounds. Most of these visiting sharks only stay during the warm summer months, but researchers believe a small percentage find enough to eat to keep them in Alaska year-round.

Great whites are related to salmon sharks. Like salmon sharks, great whites have a highly developed countercurrent heat exchange mechanism that allows them to maintain a body temperature several degrees warmer than the ambient temperature. Sharks in this family represent some of the few species of endothermic fish in the ocean. Unlike their cold-blooded cousins, great whites and salmon sharks can produce bursts of speed to chase down prey, even in frigid ocean temperatures.

In recent years, Alaskans living and working in the far north regions of the Bering Strait and the Chukchi and Beaufort Seas have reported sightings of marine mammals with unusual wounds. Researchers noted that several ice-associated seals and Steller sea lions in the area suffered injuries from an uncommon predator.

Reports of seals with amputated flippers alerted biologists because killer whales have pegged teeth and don’t cause a slicing-type laceration. In some instances, scientists noted penetrating stab wounds and circular bite marks. Flesh torn by sharp, triangular teeth convinced researchers they were looking at the bite marks of a very large shark. Are the warming water temperatures and melting sea ice inducing great white sharks to travel further north where they can find a bounty of sea mammals to eat?

When great white sharks reach adulthood and grow very large, they seem to prefer eating marine mammals over fish, probably because marine mammals have a high energy-rich fat content. Observers have watched great whiles kill beluga whales in Cook Inlet, and biologists suspect they may even take walruses in the Bering Sea and the Arctic Ocean. Are great whites, at least in part, responsible for the diminishing numbers of Beluga whales? If the number of great whites increases in Alaska, will they affect other marine mammals’ population densities? Much more research is needed to answer these questions.

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I’ll take a closer look at my nemesis, the spiny dogfish shark, in my next post. We used to catch one or two of these nasty little critters a year during our summer fishing trips, but we caught as many as twenty per day this past summer. Is this increase in spiny dogfish a trend, or was this past year only an anomaly?

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.