Sharks often capture human imagination, but widely recognized species like the great white do not represent the majority of shark populations. Many assume the most famous sharks are also the most numerous, but ocean abundance tells a different story. Understanding which sharks truly thrive in large numbers helps paint a more accurate picture of marine ecosystems.
The Most Abundant Shark Species
The Spiny Dogfish (Squalus acanthias) is considered the most common shark species in the world’s oceans. Its widespread presence stems from its ability to inhabit a broad range of marine environments globally. Found throughout temperate and subarctic waters, its populations are extensive, particularly in the North Atlantic and North Pacific oceans. This adaptability contributes to its abundance across vast regions.
Characteristics and Lifestyle
The Spiny Dogfish is a relatively small shark, typically reaching lengths of up to 1.6 meters. Its slender body is grey to brownish on top with a paler underside, often marked with distinctive white spots. A sharp, ungrooved spine in front of each of its two dorsal fins is a unique feature, used defensively if threatened. Unlike many other sharks, it lacks an anal fin.
This benthopelagic species inhabits both the open water column and the seafloor, often found on continental shelves. Spiny Dogfish are highly adaptable, tolerating a wide range of salinities and preferring temperate to sub-arctic waters, typically between 7°C and 15°C. They form large schools, sometimes numbering in the thousands, and undertake seasonal migrations to stay within their preferred temperature ranges.
As opportunistic predators, their diet varies depending on their size and location. Smaller Spiny Dogfish feed on crustaceans, while larger individuals consume small schooling fish, squid, and jellyfish. They also scavenge on marine mammals.
Reproduction is characterized by slow growth and late maturation, with males reaching sexual maturity around 10-12 years and females between 12 and 16 years. They have one of the longest gestation periods among vertebrates, lasting 18 to 24 months. Females give birth to live young, typically producing an average of six pups per litter. This reproductive strategy contributes to their long lifespan, which can extend to 30-40 years.
Ecological Role and Human Interaction
In marine ecosystems, the Spiny Dogfish plays an important role as both a predator and prey. As an opportunistic feeder, it influences populations of various small fish and invertebrate species. Larger sharks and some bony fish prey upon them, integrating them into the broader food web.
The Spiny Dogfish has a long history of interaction with human fisheries. It has been commercially harvested for various purposes, including its meat, which is popular in Europe for dishes like “fish and chips,” as well as for its liver oil and fish meal.
However, its schooling behavior and aggregating habits, coupled with its slow growth, late maturation, and low reproductive rate, make it susceptible to overfishing. Intense fishing pressure has led to significant declines in some regional populations, such as in the Northeast Atlantic. Consequently, conservation concerns have arisen, leading to management efforts and its classification as “Vulnerable” by the International Union for Conservation of Nature (IUCN).