Squalus acanthias, commonly known as the spiny dogfish, is a widely distributed shark species inhabiting temperate and subarctic waters across the globe. This small, demersal shark is found in both the northern and southern hemispheres, making it one of the most widespread shark species worldwide.
Defining Characteristics and Where They Live
The spiny dogfish is recognized by its slender build and a grayish-brown color that fades to a pale underbelly, often adorned with rows of white spots along its upper body. It grows to lengths between 1.0 and 1.5 meters, with older females reaching up to 1.24 meters. A distinguishing feature is the presence of two dorsal fins, each preceded by a sharp, defensive spine capable of inflicting venomous wounds. Unlike many other shark species, the spiny dogfish lacks an anal fin.
These sharks inhabit temperate continental shelf seas, from shallow coastal waters to depths of 900 meters, though they are most frequently observed between 10 and 200 meters. They prefer water temperatures ranging from 7°C to 15°C and can tolerate brackish conditions, but thrive in full-strength seawater. Spiny dogfish are highly migratory, forming large, dense schools of hundreds to thousands of individuals, often segregated by size and sex.
Life in the Ocean
Spiny dogfish are generalist predators, feeding on a diverse range of prey including comb jellyfish, squid, mackerel, herring, and various benthic organisms like shrimp, crabs, and sea cucumbers. They spend winters in deeper waters, where their feeding activity might decrease, moving to warmer coastal waters in summer to forage actively. The species detects weak electric fields generated by potential prey, aiding in its hunting strategy.
This shark exhibits a unique reproductive strategy, being ovoviviparous, meaning the embryos develop inside eggs within the mother’s body, hatching internally before live birth. The spiny dogfish has one of the longest known gestation periods among all vertebrates, lasting between 18 to 24 months. Females mature late, around 18-21 years of age, while males mature earlier, at about 11 years. Litters are small, ranging from 1 to 15 pups, with an average of 6-7, and newborns measure between 20-33 cm in length.
Conservation and Human Interactions
The spiny dogfish faces conservation challenges due to its life history traits, including late maturity, slow growth, small litter sizes, and a prolonged gestation period. These characteristics make the species vulnerable to overexploitation by fisheries. The IUCN Red List has assessed the spiny dogfish as endangered globally.
Historically, this species has been of commercial importance, particularly in the Northeast Atlantic and Northwest Atlantic, as well as parts of the Pacific. Spiny dogfish are targeted for human consumption, often sold as “rock salmon” or “grayfish,” and their liver oil has been used for vitamins and other products. They are also utilized for leather, fertilizer, and as laboratory animals. Fishing large, aggregating schools, especially those composed of gravid females, has exacerbated population declines.
Conservation and management measures have been limited in many regions. Some areas have implemented catch limits, but challenges persist, particularly with bycatch in demersal fisheries where a high percentage of caught dogfish may be discarded. Sustaining populations of this species requires careful management to support long-term recovery.