Sharks‘ Whale Feast Unique Research Opportunity

November 13, 2006

Release from: Guy Rogers
The Herald (South Africa)

Great white sharks have been recorded for the first time feeding off a whale carcass in Algoa Bay, presenting excellent opportunities for research and management of this problematic marine debris.

That‘s the view of Bayworld and NMMU marine biologist and shark specialist Dr Matt Dicken, who has spent three weeks studying the activity around the carcass. He said because of its unpredictability, the event has been documented in detail only 10 times before, internationally, and only once before in South African waters, off Durban in 1998.

Having been alerted by Marine and Coastal Management (MCM) researcher George Kant about the carcass of a 15m humpback whale lying about 6km off Port Elizabeth Harbour, in the shipping lanes, he travelled out the same day, on MCM‘s vessel Lillian Ngoyi to the spot.

With help from the MCM crew he was able to attach a rope around the tail of the carcass and, having obtained permission from the Port of Ngqura, they then towed it across to the new port.

Two days later, having acquired the necessary anchor, chain and other equipment to secure the carcass, with the help of KwaZulu Natal-based dive operator Blue Wilderness Dive Expeditions, he then had it towed it out into the bay.

The dumping point where the carcass is now anchored, is being kept secret to avoid attracting lots of curious boat traffic and interfering with research. But it is a long way off-shore and about 50km from the nearest bathing beach, he stressed.

“This is much better than allowing it to drift, endangering shipping or coming in-shore where it can attract unwelcome visitors. It is also better than burying it (as some municipalities have done) below the high-water mark, where it can possibly leach out oils, which could attract sharks into coastal waters near beaches.

“I believe that the way we have done it should be established as best practice. It capitalises on the research value of the carcass, it‘s safe and it‘s pro-active. If our municipality could embrace this approach we could become recognised as the international leader in this field.”

Dicken said the first shark he spotted, a juvenile, was “skittish”, making only a few half-hearted attempts to bite the fins and tail of the whale.

“It‘s a misconception that these creatures do not have fears of their own. The carcass is very big and the shark was obviously wary about how safe it was.”

The next two, also juveniles, between 1,5m and 2m long, were very fat and had apparently been feeding on the carcass all night.

They were joined by another 2m-long white shark and the trio “dragged themselves, with a biting action, up the side of the whale, half out of the water”.

They showed a lot of interest in the researcher‘s rubber duck and one repeatedly hit the boat until two pontoons were punctured and they had to return to shore.

With relatively few sharks having been spotted and no monster-size ones, Dicken‘s preliminary reasoning is that, although sharks have acute smell the rich, oily chum line from the carcass only extends some 5km with the current and the sharks would have had to cross this line to be alerted.

Why no raggies, duskies, bronzies or hammerheads which are some of the other big sharks resident in Mandela Bay?

Apparently because of the design of their dentures as “grabbers” rather than “rippers”. Only white sharks and Zambezis, which arrive here in summer, have the bite size, power and denture design to scavenge on a whale. “But the bottom line is we know very little.

“How important are these events for their nutrition? Are they a cue for mating, as has been speculated? What sex are they? How many are down there feeding on the underside of the carcass?”

Dicken said the next step is to raise funds for and purchase ultra-sonic tagging equipment. This would help determine how long the sharks feed on the carcass and how often they return to it.