Spiny Dogfish

The Spiny Dogfish (Squalus acanthias) is a small, slender shark in the family Squalidae, among the most abundant shark species in the world and one of the most extensively studied due to its historic importance in fisheries and biology labs. It occurs in cold temperate and boreal waters across both hemispheres, often forming enormous schools segregated by size and sex. Recognized by the sharp, mildly venomous spines preceding each dorsal fin and its complete lack of an anal fin, it has one of the longest gestation periods of any vertebrate. Some regional populations have experienced significant historic declines from overfishing, leading to Vulnerable status in parts of its range.

Key field marks:

• Slender, gray body with scattered white spots along the back, fading with age
• Sharp spine at the leading edge of each of the two dorsal fins
• No anal fin, a key distinction from similar-sized requiem sharks
• Pointed snout, large eyes
• Small size, typically under 1.2 m

The combination of dorsal fin spines and the absence of an anal fin reliably identifies this and other dogfish species.

Found in cold temperate to boreal coastal and shelf waters worldwide, including the North Atlantic, North Pacific, and southern oceans, typically at depths from near-shore to around 200 m, occasionally deeper. Tolerates a wide temperature range but favors cooler water, often undertaking extensive seasonal migrations toward warmer or cooler water and shallower or deeper depths to track preferred temperatures and prey.

Spiny Dogfish are highly social, forming large schools often segregated by age, sex, or reproductive status, and undertake long seasonal migrations. They feed opportunistically on schooling fish, squid, and jellyfish, often in coordinated group hunting. Reproduction is ovoviviparous with one of the longest gestation periods of any vertebrate, spanning roughly 18-24 months, after which females give birth to small litters of live pups. Their dorsal fin spines provide defense against predators. As a highly abundant mesopredator, they play a significant role in structuring coastal fish and invertebrate communities.