Said to be the most abundant living shark, the spiny dogfish is a slow, inactive swimmer and forms massive feeding aggregations of thousands of individuals. Tending to be same-sex and same-size shoals, they prey on shoals of bony fish, as well as octopuses, smaller sharks, squid, crabs and shark egg cases (3). They are highly migratory, moving towards the equatorial side of their range during winter (2). With estimates of between 20 years and 75 years, the spiny dogfish is thought to be a very long-lived fish that matures late and reproduces slowly, with gestation lasting two years – the longest of any vertebrate (1) (2) (3). An ovoviviparous species, spiny dogfish develop in eggs within the female, and gain nourishment from their yolk sacs, After four to six months, these eggs are shed, but the embryos continue to develop inside the female, still living off the yolk sac attached to their abdomens. Finally, after another 18 to 20 months of development, six to seven live young are born, measuring 20 to 33 centimetres. Despite possessing venom-delivering spines on each of its two dorsal fins, the spiny dogfish is eaten by cod, red hake, goosefish, other spiny dogfish, larger sharks, seals, and orcas (2).
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