The Spiny Dogfish, also known as the Spurdog, Mud Shark, or Piked Dogfish, are the most common sharks of the world. Spiny Dogfish are a species of smaller sharks that are found off the coast of every continent except Antarctica. The Spiny Dogfish is the most populous shark in the world, but these small sharks are not what most people think of when they think of sharks. So even though they are everywhere, little is really known about them. So today we thought we’d introduce you to the most common shark in the ocean: The Spiny Dogfish.

SHARK ACADEMY: The Spiny Dogfish Shark

Who Are The Spiny Dogfish?

The Spiny Dogfish is named for the two venomous spines at the base of their dorsal fins that provide protection against predators. If attacked the Spiny Dogfish will arch its back and stick the predator with venom. The Spiny Dogfish is a smaller species of shark. At maturity males reach 2.6-3.3 feet (80-100 cm) in length, while females reach 3.23-5.22 feet (98.5-159 cm) in length. They are grey-brown with white undersides. When they are born they have small white spots along their back to camouflage them against predators that fade as they reach maturity. They have long, thin bodies with no anal fin. They have strong jaws located on the underneath side of their pointed snout that are lined with 50 teeth. Spiny Dogfish also have unusually large eyes on the sides on their head.

Where Does The Spiny Dogfish Shark Live?

Spiny Dogfish are found throughout the world. They are extremely migratory and will follow the seasons along the poles. The same shark will travel from Cape Town, South Africa all the way to the Eastern Coast of Canada. They are a bottom dwelling species found at depths of 164-499 feet (50-149 m) but have also been found over the continental shelf at depths of 2595 feet (900 m). They tend to stay along the seabed but will migrate vertically to hunt prey. They tend to prefer saltwater but can tolerate brackish waters. Younger Spiny Dogfish tend to live offshore while adult females tend to live inshore.

What Does the Spiny Dogfish Shark Eat?

Spiny Dogfish usually eat bony fish and other sharks. However, they will also eat squid, worms, shrimp, crabs, comb jellies, and octopus. Spiny Dogfish are impressive predators. They tend to attack schooling fish and have been known to attack fish that are larger than themselves. They have been observed literally eating entire schools of cod and haddock. What makes them such great hunters is that they have strong flexible jaws lined with overlapping teeth that create one solid sharp edge much like a knife. Spiny Dogfish are also very aggressive because of their poisonous spines so they will boldly assault prey without hesitation.

How Does The Spiny Dogfish Shark Behave?

For being a smaller sized shark, Spiny Dogfish are incredibly aggressive. They are also one of the most social species of shark and get their name from the fact they will hunt in large packs. These packs can be as numerous as thousands of sharks and they will attack entire schools of fish together or team up on really large prey. Even Spiny Dogfish pups will hunt in these packs. Their pack aggression is so well known that fisherman consider them a nuisance because they will bite through fishing nets to feed on the fish trapped inside. Packs of Spiny Dogfish have been known to clear out an entire fisherman’s net.

How Does The Spiny Dogfish Shark Reproduce?

The Spiny Dogfish has the longest period of gestation of any shark. Females are pregnant for 22-24 months. Mating typically occurs during the winter months in offshore waters. The male Spiny Dogfish impregnates the female with a clasper and once fertilized the eggs will be surrounded by candles. Candles are thin shells which creates an egg-like embryo. Spiny Dogfish are aplacentel viviparous which means that the shark fetuses grows inside the mother and are fed through a yolk sac. Once they reach maturity, they will be born head first with a thin cartilage cover over their poisonous spines to protect the mother. Spiny Dogfish litters range from 1 to 15, but on average 6-7 pups are born at any given time. These pups will reach maturity when the males are 11 years old and the females are 18 years old. Spiny Dogfish tend to live an average of 100 years.

What Are The Threats To Spiny Dogfish Shark?

Even with the protection of their poisonous spines, Spiny Dogfish have a few natural predators. Cod, Red Hake, Goosefish, Sharks, Seals, Killer Whales, and even larger Spiny Dogfish prey on them. Spiny Dogfish, like all sharks, also face numerous threats from humanity. Though they are the most populous fish in the ocean, they are very vulnerable to overfishing. Spiny Dogfish are fished for meat, a common bycatch, and are often killed by fisherman for threatening their catch. Since they have long gestation periods their reproduction cannot keep up with the rate of they are being fished from the ocean. So in the last two decades they have seen a 75% decline in population. They are listed as vulnerable worldwide and critically endangered in the North Atlantic by the International Union For Conservation. So even with their populous numbers, Spiny Dogfish, like other sharks of the world, are facing possible extinction.

Spiny Dogfish are the most populous sharks in the ocean, however they are not what we typically think of when we think about sharks. These smaller sharks are found throughout the planet and have some really unique characteristics. They have unusual physical characteristics like venomous spines, they hunt in packs, and they have the longest gestation period of any shark. These commonplace, but unusual sharks, highlight the diverse variety of sharks on the planet.