Poach­ing, nets see lo­cal great whites fac­ing threat of ex­tinc­tion

The loss of the sharks would see an in­crease in the Cape fur seal pop­u­la­tion, which in turn would af­fect fish pop­u­la­tions, writes SHEREE BEGA

Weekend Argus (Saturday Edition) - - NEWS -

AT FIRST, Dr Sara An­dreotti got sick. Very sea­sick. Out on a large cata­ma­ran, the shark sci­en­tist would, on her worst days, im­plore her crew to take her back to shore.

“I didn’t have my sea legs,” said the 32-year-old Ital­ian. “The mo­ment we hit the ocean, the sea­sick­ness would ar­rive – I had to drink sea­sick­ness tablets ev­ery day.”

But An­dreotti, of the evo­lu­tion­ary ge­nomics group at Stel­len­bosch Univer­sity’s botany and zo­ol­ogy depart­ment, was liv­ing her dream: study­ing great white sharks.

On the cata­ma­ran, equipped as a re­search ves­sel and loaned by world-fa­mous shark cage diver Michael Rutzen, An­dreotti would spend months-long voy­ages at sea, cruis­ing Gansbaai and South Africa’s vast coast­line, search­ing for great white sharks and count­ing them all on a shoe­string bud­get.

The sea has al­ways called to An­dreotti; she worked as guide for a nat­u­ral marine re­serve in Italy when aged 16. Her fas­ci­na­tion brought her to South Africa in 2007, where she en­coun­tered great white sharks and fell “in love with these mag­nif­i­cent an­i­mals”.

“Ev­ery­one has a mis­con­cep­tion that the great white is a mind­less killing machine, but that is not the case,” she said. “They ap­pear to think about ev­ery­thing they do. Of course they are for­mi­da­ble preda­tors, but that doesn’t mean they’re tar­get­ing hu­mans like peo­ple be­lieve… It’s very stress­ful if you con­sider you want to spend your life study­ing them.”

But it’s South Africa’s great white sharks, not its hu­mans, that are in dan­ger­ous waters.

This week An­dreotti re­vealed the re­sults of the ground­break­ing six-year study she led; there are only be­tween 353 to 522 in­di­vid­ual such sharks left off South Africa.

The iconic species is on the brink of ex­tinc­tion. “The chances for their sur­vival are even worse than what we pre­vi­ously thought,” she warned. “Their num­bers might al­ready be too low to en­sure their sur­vival.”

Her pi­o­neer­ing re­search, re­cently pub­lished in the jour­nal Marine Ecol­ogy Progress Se­ries, was con­ducted with Rutzen – who helped An­dreotti lo­cate the sharks – and the Depart­ment of En­vi­ron­men­tal Af­fairs. It rep­re­sents the largest field re­search study on South Africa’s great whites un­der­taken to date.

Our great white pop­u­la­tion is in “dou­ble jeop­ardy” – not only are their num­bers wor­ry­ingly low, but they have the low­est ge­netic diver­sity of all great white shark pop­u­la­tions world­wide.

An­dreotti and her fel­low re­searchers blame the im­pact of shark nets and baited hooks in KwaZulu-Natal, poach­ing for shark jaws, habi­tat en­croach­ment, pol­lu­tion and the de­ple­tion of food sources for the sharp de­cline.

Rutzen, who is known as “Shark­man” for his epic free-dives with great white sharks to dis­pel the myth they are man-eat­ing mon­sters, agreed. “In the 1990s, it was not un­com­mon to have 20 great whites around our boats. We’re lucky these days if we have be­tween one and three… Shark nets are not a pro­tec­tion de­vice, but a killing de­vice.”

The end of great whites will af­fect the eco­log­i­cal sta­bil­ity of South Africa’s marine en­vi­ron­ment. “A de­crease in white shark num­bers will lead to an in­crease in the Cape fur seal pop­u­la­tion, which in turn will have an im­pact on fish pop­u­la­tions and thus on fish­eries,” notes the pa­per.

Be­tween 2009 and 2011, An­dreotti and Rutzen col­lected nearly 5 000 pho­to­graphs of the dor­sal fins of white sharks fre­quent­ing Gansbaai, a shark hotspot. The notches in dor­sal fins are like a unique fin­ger­print with a spe­cific num­ber of notches on their trail­ing edges. The re­searchers had to be sure the sharks, who all have “dif­fer­ent per­son­al­i­ties”, got close enough to their boat to take a clear pic­ture of the dor­sal fin and to col­lect a biopsy for ge­netic anal­y­sis.

Ac­cord­ing to An­dreotti, there are now 52 per­cent fewer than es­ti­mated in pre­vi­ous sim­i­lar stud­ies.

Us­ing chum to lure the sharks to their boat was very “dodgy”, said An­dreotti. “They see the head of a dead tuna run­ning away from them… that’s prob­a­bly some­thing they have not seen in their lives and they prob­a­bly don’t like it.”

They had to be cer­tain the sharks they iden­ti­fied and counted in Gansbaai were rep­re­sen­ta­tive of the en­tire white shark pop­u­la­tion. So they set sail again, spend­ing another four years sail­ing along the coast­line, col­lect­ing biopsy sam­ples and snap­ping photos of dor­sal fins.

“The sub­se­quent ge­netic anal­y­sis then proved that there is only one pop­u­la­tion and that the same sharks are roam­ing the coast­line,” said An­dreotti.

Her ge­netic study shows an ef­fec­tive pop­u­la­tion size of only 333 in­di­vid­u­als. “The thresh­old is cal­cu­lated at 500 for other species to pre­vent in­breed­ing de­pres­sion. If that ap­plies to white sharks, we’re al­ready in big trou­ble be­cause my es­ti­mates don’t even reach 350.”

Be­tween 1978 and 2008, 1 063 white sharks were killed in shark pro­tec­tion mea­sures, she said. “We can’t be pro­tect­ing sharks on one side and killing them on the other. Ev­ery time a shark comes too close, we kill it. Hu­man be­ings need to change their at­ti­tude to­wards the oceans. There are co­bras on moun­tains, but we still go hike there. The sooner we start look­ing at sharks in the same way, the better.”

Stel­len­bosch Univer­sity has de­vel­oped the Shark­safe Bar­rier, an en­vi­ron­men­tally friendly ar­ti­fi­cial mag­netic kelp, which may be im­ple­mented in De­cem­ber, said Rutzen. Sharks are re­pelled by mag­netism.

Shark nets “are some­thing we should stop to­mor­row”.

“But pol­lu­tion and man­age­ment of the food sources is some­thing that will take much longer to be fixed, as well as poach­ers, who are al­ways dif­fi­cult to con­trol,” An­dreotti said.

There is a move to in­clude great whites on Ap­pen­dix 1 of the Con­ven­tion on In­ter­na­tional Trade in En­dan­gered Species of Wild Fauna and Flora, in Septem­ber, which will af­ford white sharks greater pro­tec­tion. An­dreotti said un­der­stand­ing pop­u­la­tion dy­nam­ics can play a crit­i­cal role in de­vel­op­ing con­ser­va­tion strate­gies for species in peril.

“We must do what we can while we can,” said Rutzen, who fore­sees the im­mi­nent demise of the lo­cal cage div­ing in­dus­try. “Our great whites are fac­ing a tough bat­tle. Now we know from our re­search what the facts are, so we can hope­fully help save them.”

Un­til their study, said Rutzen, most con­ser­va­tion ef­forts were based on “gut feel­ings and peo­ple’s per­cep­tions”. But the bleak find­ings have also caused some con­tro­versy. On the univer­sity’s Facebook page this week, users like Greg Keller­mann wrote that shark num­bers had ex­ploded and he “still can’t un­der­stand the mo­ti­va­tion for claim­ing their near ex­tinc­tion”.

An­dreotti said: “Sim­ply put, see­ing a shark 20 times does not mean there are 20 sharks.

“This is the largest photo iden­ti­fi­ca­tion and ge­netic data­base of great white sharks in South Africa, and will serve as the bench­mark for fu­ture ob­ser­va­tions and the con­ser­va­tion of this top preda­tor.” sheree.bega@inl.co.za


A study says there are only be­tween 353 to 522 in­di­vid­ual great white sharks left around South Africa and the species is on the brink of ex­tinc­tion.

Shark re­searcher Dr Sara An­dreotti.

Newspapers in English

Newspapers from South Africa

© PressReader. All rights reserved.