This week's Top Ten list is dedicated to a species of shark that swims under the radar but certainly deserves a moment in the spotlight: the blue shark (Prionace glauca).
The amazing images below come from photographer Albert Ollé Callau, who snapped them during a dive off Pico Island in the Azores archipelago. He says of the experience: "Shark diving is one of the best feelings I've experienced at sea, being a part of the vastness of the Atlantic Ocean. I had good visibility and it was the perfect scenario for observing these large predators. The blue sharks were very curious, approaching me and even brushing against me several times with their fins. It was truly a unique experience."
Yes, we had to mention the obvious – these sharks are blue. Their stunning skin ranges from a distinct deep blue on top, to bright-blue sides and a crisp-white underbelly. This contrast in colours is known as countershading and provides camouflage for the shark in the open ocean!
Blue sharks are truly cosmopolitan. In fact, the IUCN lists the waters of over 150 countries as their native habitat! These worldly circumnavigators can be found in tropical and temperate waters from as far north as Norway all the way down to the tip of South America! They're also highly migratory, and have been tracked swimming over 9,000 kilometres (5,592 miles) during pupping season!
The blue shark was originally named Prionace glauca by naturalist Carl Linnaeus in 1758. Prionace is derived from the Greek word 'prion' (meaning 'saw') and 'akis' (meaning 'point'). Its long, conical snout is longer than the full width of its mouth and, combined with extremely long pectoral fins, lands them firmly in the 'string bean' crew.
Don't let that slender body fool you, blue sharks are phenomenally evolved swimmers. Their sleek silhouette makes them incredibly graceful cruisers (perfect for long migrations in the open ocean) and agile hunters – a must when chasing quick prey like squid and other cephalopods.
In general, blue sharks are opportunistic feeders, but they're known to munch squid whenever (and wherever) they can – and that countershading we talked about helps them do it! In 2013, a male blue shark nicknamed 'Bohdi' plunged his way into the records books after making the deepest known blue shark dive at 1,250 metres (4,101ft) in search of an inky meal!
Contrary to popular belief, great whites aren't the only sharks with Air Jaws-style jumping capabilities. Blue sharks have also been spotted performing out-of-water acrobatics when chasing prey!
Though some species of shark don't reach sexual maturity for decades, blue sharks are surprisingly quick growers. By six years of age, both male and female blues will be ready to reproduce! Speedy baby-making means that they're not as badly affected by fishing pressures, which plague many other species.
Blue shark lovin' isn't the sweetest of soirees ... the skin of females has to be three times thicker than that of males to withstand extensive courtship biting. Luckily, females can store sperm for later use in special glands. After a nine-to-twelve-month gestation period, female blue sharks give (live) birth to large litters of pups – the largest ever recorded was 135 (shark pup squee!).
Blue sharks have to live with a motley crew of body-squatters: parasitic copepods. These tiny animals are known to target blue sharks specifically, commonly latching on to the pectoral fins, burrowing in the olfactory (nose) sacs, living on the skin or hiding out in the gills. A single shark can carry up to 3,000 individual parasites, with some carrying over five different species at any given time! Any fish with that many parasite problems gets a sympathetic hat tip from us.
Perhaps the most important thing to take away from this blue shark meet-and-greet is that, like all sharks, blues play an important role in ocean ecosystems and deserve just a bit more of our attention. The species might be in good shape for now, but its future success hinges on us maintaining sustainable fishing practices.
Check out more photos from Albert Ollé Callau here.
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