Electric blues
Blue sharks aren’t just fast, formidable hunters. They are also puppylike and astonishingly beautiful, fifififinds the BBC’s Ellen Husain, who dived with them offff Cornwall.
Meet the pretty sharks found off Cornwall
There are many adjectives commonly associated with sharks in our post- Jaws society: fearsome, toothy, voracious… killers. But not usually pretty. However, having just spent water-time with blue sharks, the overwhelming impression I’m left with is just how pretty they are.
Their slender bodies glide and bend in the water, giving these fish an incredibly graceful form, and they really are blue. Not blue from the colour cast of light filtered by seawater, but actually a bright – at times almost electric – blue. To top it all off, they have a huge cartoon-eye and a rather friendly face. If Disney made sharks, they’d make blue sharks. They’re also curious, but even when they’re bumping off the dome of my camera they don’t feel a threat. The species makes a new addition to my growing list of ‘favourite’ fish.
“They remind me of puppies,” says Charles Hood, as we peer over the edge of his boat, getting our first look at a small four-footer that’s just shown up. Charles has been running small boat trips for 10 years, and has honed the art of finding these sharks in the open ocean.
Twenty kilometres out to sea from Penzance in
Cornwall, we’ve already run into common dolphins hunting a fish bait-ball. Gannets diving from on high while the mammals converge at the surface, sending up tracks of white water. It is the kind of spectacle you only get when there are lots of fish to be had. We see around 20 dolphins at any one time, but there must be at least 80 or more, most of them hidden below, rounding up the fish beneath the surface.
We are not yet at Charles’ preferred spot, but with so much action he decides to try where we are. “You often find blue sharks around dolphins. I think they’re drawn to the commotion – they pick off the fish that the dolphins herd,” he says. When he stops the engine we receive another treat as eight dolphins head straight for the boat at top speed, veering under and around us, buzzing us so loudly that we can hear their sonar through the rubber hull. As a wildlife film-maker, I’ve got used to journeying to the opposite corners of the Earth for this sort of action, so it is wonderful to see it in the UK. We’re here for a new blue-shark research project conducted by Andrea Gaion and his colleague Karl O’Neill. Andrea previously worked with great whites off South Africa, and hopes to bring the same minimally invasive field methods to study the blue sharks that are becoming increasingly well known off Cornwall. “Cornish seas are very productive over the summer, and we want to see if the same populations of sharks gather every summer to feed,” Andrea says. His study aims to take skin biopsies from sharks in the water – without needing to stress the fish by catching and landing them on the boat. He will also generate a photo ID database of shark dorsal fins.
BUILDING A FAMILY TREE
Genetic analysis of the biopsies will be used to assess how closely related the animals are. And Andrea and his team will look at bioaccumulation of contaminants such as PCBs (industrial products or chemicals) to see if pollutants are affecting their fitness. “As top predators, blue sharks can build up a lot of toxins in their bodies,” says Andrea.
Many people may be surprised to know large numbers of sharks congregate off Cornwall, albeit many miles out to sea, but research over the past decade has revealed these waters to be a hotspot. Prof David Sims of the Marine Biological Association of the UK has a lab group that studies blue sharks as part of the Global Shark Tracking Project. Along with Dr Nuno Queroz, and others, recent studies using ‘smart tags’ to relay positions and other data to satellites have revealed that the blue sharks visiting Cornwall can travel an extremely long way.
“IF DISNEY MADE SHARKS, THEY’D MAKE BLUE SHARKS. EVEN WHEN THEY’RE BUMPING OFF THE DOME OF MY CAMERA, THEY DON’T FEEL A THREAT.”
“Our team has tracked blue sharks off Cornwall migrating south all the way back to waters off Spain, Portugal and West Africa,” says Sims. In fact, blues are truly oceanic sharks, favouring deep water; they are possibly the most wide-ranging sharks of all. Preferring temperate and subtropical waters at 12–20°C, they nonetheless tolerate seas as cold as 8°C and up to bathlike 29°C, and are fairly global in distribution, excluding high latitudes and the poles.
“We’ve tracked several amazing journeys,” Sims says. “Perhaps the most surprising involved large females, including pregnant ones, migrating south from waters off Canada to productive parts of the ocean off South America and West Africa. Maybe this was to give birth – the whole Atlantic is their home range.”
Though the movements of individuals vary greatly, as a population North Atlantic blue sharks are highly migratory. They follow a broadly clockwise circulation throughout the year, taking advantage of major ocean currents. Their annual schedule seems quite enviable. Riding the Gulf Stream east from North America to the waters off Europe in spring, they remain with us over summer before heading south, many via the Canary Islands and Azores. Then they head back west on the Atlantic North Equatorial Current to the Caribbean in winter.
TAKING ADVANTAGE
If you’ve been watching BBC One’s Blue Planet II, you’ll be well aware that oceanic waters are often thought of as food deserts – where resources are patchy in space and time, often with scant nutrients between food oases. Like other open-ocean sharks, such as oceanic whitetips, blues are phenomenally opportunistic. They seek out food over huge distances. According to Sims, their arrival in UK waters in
THIS IS ONE OF THOSE GREAT DAYS ON THE WATER. NOT LONG AFTER STOPPING WE SEE OUR FIRST BLUE SHARK.
spring and early summer is timed to feed on schooling fish such as mackerel in our seasonally rich waters.
Blues show up in large numbers at various other annual bonanzas around the world, including southern Africa’s famous ‘Sardine Run’ and the spawning of squid off California. Stories abound of them eating without restraint, feeding to absolute capacity and even regurgitating food only to begin eating again. Sims’ group has revealed that North Atlantic blue sharks follow ocean fronts – areas of water mixing and high productivity that tend to support a lot of fish life.
One such area is the tidal-induced front at the mouth of the English Channel, between Penzance and France – Andrea’s study site. Finding the sharks involves bait, but no hooks: simply hanging a perforated bucket of nicely aged and stinky fish, known as chum, in the water. It’s just a few kilograms of fish heads, tails and guts, but the oils released spread into a vast microfilm plume across the ocean surface, a fragrant elixir seemingly irresistible to any blue shark within miles.
‘Chumming’ is also widely used by boats carrying birdwatchers in search of pelagic seabirds such as storm-petrels and shearwaters. It can be controversial, usually when it consistently attracts sharks to a certain area, changing their behaviour, or causes them to associate food with divers or boats. But in this case, it’s so infrequent it is unlikely to cause any issues.
Before my trip, I was warned by Charles to take seasickness pills. “It could take one to two hours for the sharks to show up,” he told me. Bobbing for hours in the open sea in a boat reeking of old fish is a recipe for nausea. But this is one of those great days on the water. Incredibly, fewer than 15 minutes after stopping we see our first blue shark. Within another quarter of an hour there are at least six around and under the boat. Agile, iridescent blue streaks in the water, most are small, but there’s at least one seven-footer.
SWIMMING WITH SHARKS
As I pull on my wetsuit, Charles assures me the sharks are a pleasure to dive with. “They’re curious, but not aggressive.” Slipping into the water, I’m greeted by a couple of smaller animals around my fins. Trying not to kick them, I wait for my camera to be handed over the side of the boat. Underwater the sharks do not disappoint. They’re not remotely shy – coming at and over the camera, too close to focus at times.
These are, without doubt, the most graceful sharks
I’ve seen. Again, it’s their iridescent blue skin that really fascinates. It actually seems to glow, and reflects the sea’s lensing sunlight with such vivid definition that I wonder about its optical properties. The sharks are a pleasure to swim with; there’s no hint of aggression.
As the numbers build, Andrea is keen to get going with the biopsy work. So once I’m out of the water, it’s action stations on the boat. A special biopsy tip is mounted on a spear gun, designed to take a small core of tissue 0.7cm x 1.5cm long. Andrea assures me that this will not harm the sharks and that they’re used to far worse injuries from each other during mating. But despite repeated attempts and a perfect angle for the dart, it stubbornly refuses to penetrate their skin.
The sharks appear unperturbed by the dart’s impact – the same individuals come to the boat repeatedly. Andrea explains that the sharks seen here are usually juvenile males or adult females. His aim is to sample only the adults, where the biopsy is relatively much smaller compared to the size of the animal (and therefore has less impact), but this brings with it a problem. “The females are very thick-skinned,” he says. “They have to be for mating – the males bite them. Seriously, their skin is up to three times thicker.”
It’s disappointing, but fieldwork is often like that in the real world. Techniques have to be developed, and today’s trip is part of a process that will lead to successful biopsies and new data. Andrea is wise to be starting gently, before increasing the power he uses to penetrate sharkskin and obtain samples.
INDIVIDUAL IDENTITY
At least the large gathering of sharks and their proximity to the boat has been perfect for taking ID photographs. According to Charles, the average number seen is between five and eight, but today we have at least 20. Carl’s dorsal-fin photos will go into a database for computer analysis. To the untrained eye one shark dorsal fin might look much like another, but to specially designed software they are unique.
Using fin shape, and other distinguishing features such as pigmented ‘freckles’ and thickness of shading around the dark edge of the fin, the program will search for matches between different images. Comparing dorsals from different years and locations will then tell Andrea if there are any repeat visitors. Watching the beautiful sharks as the light plays on their skin, I can’t help hoping he gets a lot of matches.
It is late September, near the end of the season, and these sharks will leave soon. They will potentially travel as far as the Azores, running the gauntlet of long-lines and other fishing vessels on their way. I hope they make it back next year, but sadly I know for many the odds are against it.
USING FIN SHAPE AND OTHER FEATURES SUCH AS ‘FRECKLES’, THE PROGRAM WILL SEARCH FOR MATCHES.