NAME: Blue Shark
SCIENTIFIC NAME: Prionace glauca

STATUS:  Near Threatened and Critically Endangered in the Mediterranean

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POPULATION DECLINE: Blue sharks are true nomads of the open ocean, found all over the globe. These sleek swimmers can dive to incredible depths of 1,000 metres and glide effortlessly through the water with their oversized pectoral fins. They’re the ocean’s bluest shark, with iridescent skin that shifts from electric blue to violet in sunlight, and their metallic golden noses and eyes are nothing short of mesmerising.

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SIZE: At birth: 35-44cm. Mature males: 182-218cm. Mature females: 182-221cm. Max size: 384cm

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DISTRIBUTION: These sharks are the ultimate ocean nomads, roaming temperate and tropical waters across the globe. True masters of adaptation, they thrive in temperatures ranging from a chilly 7°C to a toasty 25°C. They are versatile voyagers! ​

HABITAT: These pelagic sharks cruise the open ocean, typically staying near the continental shelf between 0-1000m, diving deeper in warmer waters and migrating with the ocean currents. Some have been seen to migrate up to 9200km. Juveniles favour offshore nurseries as they grow, with a significant pupping ground found along the south coast of the UK.​

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DIET: Blue sharks are one of the few non-filter feeding sharks that munch on krill. They also feast on fish, squid, and cephalopods, but their appetite doesn't stop there. They've been known to snack on other sharks, whales, porpoises, and seabirds. When whale carcasses drift offshore, you'll often find blue sharks feeding on them in large numbers.

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BEHAVIOUR: Blue sharks are one of the most curious and beautiful sharks to share the water with, making them a popular species for diving. Their natural curiosity and quick response to bait has made them a top choice for eco-tourism. As a result of their charming personalities and curious behaviours, several locations now offer blue shark tourism, including South Africa, the Azores, and the UK.

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BIOLOGY:  

- Viviparous: Blue sharks nourish their young in the uterus via a placenta before giving birth to live pups.
- Litter size: Females can have 4–135 pups in one litter, but typically have 25-35.
- Gestation: Lasts 9–12 months, with pups born at 0.35–0.5m.
- Sexual Maturity: Males mature at 4–6 years, females at 5–7 years. Females may breed annually or every other year.

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THREATS: Blue sharks are one of the most exploited shark species worldwide, with their fins in high demand in Asian markets. They're likely the most frequently caught large shark across the oceans, thanks to their transoceanic migrations, which bring them into the sights of numerous fisheries. Caught in high seas target fisheries and as bycatch in longline, and gillnet fisheries (especially those targeting tuna), blue sharks have faced population declines of up to 80% in some areas. They’re also targeted in recreational fisheries, where post-release mortality is low, but they’re often kept. With most catches coming from the high seas, blue sharks are under immense fishing pressure both nationally and internationally.

FUN FACTS

- Blue sharks are supermums, having anywhere from 4 - 135 pups in one litter! 

- Blue sharks are one of the few non-filter feeding sharks that munch on krill

With electric blue on top and a white belly, they use countershading to blend in perfectly, the ultimate open ocean camouflage.

REFERENCES

- “Blue Shark.” Save Our Seas Foundation, https://saveourseas.com/worldofsharks/species/blue-shark
- “The IUCN Red List of Threatened Species.” IUCN Red List of Threatened Species, www.iucnredlist.org/.
- David A. Ebert. et al, 2021, Sharks of the World: A Complete Guide.