A passion for whales and creatures of the deep has taken researchers close to the belly of the beast, writes Claire Keeton

It's not every day whales break up your party. Not unless you are marine biologist Dr Sean O'Donoghue out swimming with sharks during the annual sardine run as part of research into shark behaviour during this natural phenomenon.

Tens of thousands of whales, dolphins, sharks, sailfish and gannets are among the predators that follow huge shoals of breeding fish along South Africa's east coast from June to August - in an oceanic migration that, in terms of biomass, is compared to the wildlife migration in Tanzania's Serengeti Park.

O'Donoghue, 41, has had frequent close encounters with whales and sharks while tracking Bronze whaler sharks. Early in July, off the coast of Port St John's, a pair of humpbacks swam through the fish-feeding activity and a "massive kick" of a whale's tail destroyed the "baitball" where he was diving.

On another occasion, he stared down the open mouth of a Bryde's whale, which is big enough to swallow a man - although the creature is unlikely to be that clumsy, says O'Donoghue. The whale almost landed on him while he was underwater trying to identify fish big enough to be inserted with shark tags and act as bait.

"I was alone about 4m down with sharks all around - dusky sharks, bronze whalers and black tips - and I looked up and saw a big whale with its pleats fully extended for feeding above me. It made a lunge and landed next to me. It was a lovely experience, but it was also scary because I could have been knocked unconscious."

A surfer for 30 years and a diver, O'Donoghue seems unconcerned about this narrow escape and has no fear of the sharks he is studying. Instead, the slip-slop-wearing beach boy points out that the "coppers" are nervous of humans in the ocean.

"When we were observing them, they seemed to spend a lot of time below the baitball not feeding. We were not sure if that was an effect of us being there - because sharks are scared of divers. We wanted to see what they were doing without affecting their behaviour and that's why the ultrasound transmitting tags were great," says O'Donoghue.

Professor Vic Peddemors from Australia's New South Wales Fisheries led the team including O'Donoghue, from the University of KwaZulu-Natal's School of Biological and Conservation Science, and Australian shark biologist Will Robbins.

O'Donoghue says: "The project started in 2003 to try to understand the ecological, social and economic importance of the sardine run to the east coast with surveys of how the sardines moved up the coast and under what conditions."

The 2010 study, conducted over a fortnight, got off to a slow start with days cruising the ocean looking for solid baitballs. With dire weather forecast, the team headed inland to watch Japan beat Denmark at a soccer match in Rustenburg.

On other blustery days, skipper Rod Hastier had a break, and the researchers collected data on the spawning sardine, mackerel and the abundant west coast roundherring. These fish are part of the "sardine" run. When they braaied some roundherring, O'Donoghue called his daily blog post "Eating our Science" and recommended it as delicious.

For O'Donoghue, a most precious moment was watching an iridescent striped gamefish close up - until the humpbacks came along. Also, before the sardines showed up, he witnessed the arrival of hundreds of bottlenose and common dolphins in small pods.

"They were swimming more or less in a line, and then all those in the line suddenly turned to be perpendicular to the shore like a net," says O'Donoghue, who has seen superpods of up to 5000 dolphins in previous years.

The smell of sardines, oil slicks on the water and sardine in the stomachs of gamefish confirmed to the researchers that the sardines were present early last month. But they had few occasions when the predators rounded up the fish into baitballs as big or bigger than the boat.

O'Donoghue says: "When predators feedon baitballs it seems like a crazy free-for-all, but our data shows the feeding is a lot more structured. The common dolphins will corral the fish to the surface and keep the baitball tight. When they attack, the birds dive using this attack. The sharks seem to spend a lot of time below. We wanted to see the average time the sharks spent feeding and swimming."

Finally the researchers got results - and next year they plan to go further by putting critter cams on the sharks and satellite tags on the gannets.

Sardine Fever

The ocean was calm last week when I flew into Durban for a day of sardine chasing with Sean O'Donoghue. East Coast Radio reported sardines off Virginia beach that morning and we got there by 10.30.

The scent of sardines reached us before we saw them and sardine fever was running high with crowds on the beach. We met fisherman Adrian Mariah hawking a dozen freshly netted sardines for R30. With a shark tattoo on his arm, he showed us a crate of fish for R500.

"This is only my third netting this season," he said of the high price. Fishermen on the beach confirmed the sardines - dark shapes shimmering out past the breaking surf - had been scarce so far. Past the waves gannets were exploding into the sea, catching fish.

Leonard Pillay, a fourth-generation netter, said: "The sardines have not been stable or compact like years back. Sometimes we had shoals as far as the eye could see. In the old days there was a blackness on the water and we knew in June-July the 'sards' were here.

"These days, they are staying more off-shore and moving fast. But our equipment is better today. We used to use rowing boats; now we have motorised boats. Diving to take out nets that got stuck on the rocks, we would see monster sharks swimming past. They were not at all interested in us," says Pillay.

Angler Brad Grobbelaar said he was using the sardine run to tag and release sharks for the Oceanographic Research Institute. "We see raggies, greys, hammerheads and Zambezis."

On the beach, Rynhart Kruger from Pretoria has been chasing sardine sightings for five days. "When I was a child we would see ladies scooping up sardines with their dresses," he says. "Now we have been up and down the coast but we keep just missing them."

On our last stop at Umhlanga Beach, I saw a glimpse of a fin in the distance and two rafts of floating gannets digesting their sardines. - Claire Keeton

SOMETHING FISHY : WHAT THE SARDINES DO

About 30000 tonnes of spawning sardines move northwards from the east Agulhas bank, off the coast of Port Elizabeth, to the KwaZulu-Natal seas when the continental shelf temperatures cool down to their preferred 14-20° C. Along the KZN South Coast, the sardines tend to move towards shore because they encounter warm water from the Agulhas Current, with slightly cooler water nearer the beach, which they prefer.

THE BRONZE WHALER SHARK

The Bronze whaler shark, scientifically known as Carcharhinus brachyurus, is named after its colour. This shark is a powerful fighter and can jump clear out of water. Bronze whaler sharks prefer temperate and subtropical seas. They give birth to live young, bearing 7 to 20 pups. The "coppers" grow to 3m and can weigh between 250 and 350kg.

WHAT THE SHARKS DO

The team tracked three "coppers" of up to 2m-long, observing frequent changes of depth, with the sharks swimming up to feed on fish where the shoals were detected. "Our tags showed they could navigate precisely to a baitball from a distance of at least 1km, which shows how sensitive sharks are to feeding," says Sean O'Donaghue. - Source: www.worldofsharks.net