Spiny Dogfish

Fascinating facts about the Spiny Dogfish

• A 24-month pregnancy makes the spiny dogfish one of the longest-gestating vertebrates on Earth, and each winter the female releases just 2-12 eggs that hatch inside her before she gives birth to about 5-6 live pups. This slow, internal development explains why the species bounces back so slowly after heavy fishing.
• Males can start reproducing at around ten years old, reaching only 60–65 cm (24-26 in) long, while females need about sixteen years and grow to 80-84 cm (31-33 in) before they can spawn.
• Pack hunting can involve thousands of individuals, allowing these bottom-dwelling sharks to tackle a varied menu that includes squid, fish, crab, jellyfish, sea cucumber and shrimp. Such coordinated feeding lets them dominate the temperate seas where they live.
• Vertebral and spine analysis suggests they can live up to 54 years, with some individuals reaching nearly 70, yet the average lifespan is only 30-40 years. Their long lives combined with late maturity make them especially vulnerable to over-exploitation.
• From 2000 to 2008 global catches fell from 31,700 to 13,800 tonnes, and today they are listed as Vulnerable worldwide and Critically Endangered in the Northeast Atlantic, meaning European stocks have dropped by at least 95%. These numbers illustrate how a once-abundant shark can teeter on the brink when demand outpaces biology.

At a glance

About the Spiny Dogfish

The spiny dogfish (Squalus acanthias) glides through temperate seas with a sleek, grey-brown silhouette, its back speckled with white spots and its two defensive dorsal spines, one before each dorsal fin, ready to inject a mild venom when threatened. A heterocercal tail, with asymmetrical lobes, propels it through the epipelagic zone at depths of 50–149 m, though individuals have been recorded deeper than 700 m. This bottom-dwelling boreal-temperate shark hunts in massive packs that can swell into the thousands, ambushing squid, fish, crab, jellyfish, sea cucumber, shrimp and other invertebrates with a relentless, aggressive drive. One of its most surprising traits is its extraordinarily long gestation: females carry embryos for 18 to 24 months, birthing live pups, usually five or six per litter, after the eggs develop ovoviviparously inside a protective "candle" capsule. Males reach sexual maturity around ten years, measuring 60–65 cm, while females take about sixteen years to mature, growing to 80–84 cm. Lifespans average 30–40 years, with some individuals living nearly 70. Their countershaded bodies, claspers in males, and the yolk-sac-fed embryos illustrate a lineage finely tuned to the cold, offshore waters where they spawn in winter, then release the young into deeper, warmer realms beyond most predators' reach, continuing a life cycle that has persisted since the Miocene, 11 million years ago.

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