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.

BBC Wildlife Magazine - - Contents -

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.

Clock­wise from top left: in the east At­lantic the blue shark is found from Nor­way to South Africa ( pic­tured); Above: the blue shark’s tail or cau­dal fin pro­vides swim­ming power. Left: blue sharks swim un­der Charles Hood’s boat in Pen­zance, at­tracted...

Blue and mako shark fins at a shark-finning camp in Mex­ico.

Far left: th­ese two sharks are likely to be male and too small for biop­sies to be taken. Left: Charles ( left) and Andrea ( right) in­spect the tip of the biopsy dart. Above: a blue shark joins in the feast dur­ing South Africa’s ‘Sar­dine Run’.

ELLEN HU­SAIN is a diver, pho­tog­ra­pher and BAFTA-win­ning TV pro­ducer who worked on BBC One se­ries The Hunt.

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