Did you know that there are sharks where females have got skin three times as thick as males? That is the blue shark. During mating, the male bits the female, thus one can distinguish the mature female blue shark by their scars from the male. Males maturing at 4-6 and females at 5-7 years, their lifespan is about 20 years. Blue sharks are ectothermic, that means, unlike for instance the salmon shark, blue sharks cannot elevate their body temperature above that of the surrounding water but have to rely on environmental heat sources. Blue sharks have got an nictitating membrane (translucent third eyelid) to protect their eyes and papillae on their gills to filter plankton.

Blue shark are probably the most widely spread shark specie. They are highly migratory (up to 12.000 kilometer) and live in the open sea. After being fed with a yolk-sac placenta for 12 month, about 35 (up to 135) living young are born. They start little at 35-50 cm (1.1-1.6 ft) long, but grow quick and end up at about 3.8 m (12 ft) long. This high reproduction rate is atypical for sharks, but seems necessary in the open sea without the possibility of sheltering nursing sites. Therefore, blue sharks are only considered “near threatened” on the IUCN red list.

Blue sharks are a major target of high-seas sport fishermen. Additionally, it is estimated that 10 to 20 million of these sharks are killed each year, mostly as bycatch of longline and driftnet high seas fisheries. Between 2000 and 2012, approximately 13 million blue sharks have been landed from the Atlantic by the EU fleet (the number tripled since 2002). There is no catch limits or management of any sort regarding blue sharks in Europe, unlike on the east coast of the United States and Canada. Sometimes blue sharks are purposefully captured for their fins, skins or liver oil, sometimes for their meat. It is edible, but ammoniates quickly and contains dangerous amounts of lead.

Sources: herehere and here

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