Scientists are intrigued by photographs of a killer whale attack on Cape fur seals about 15 miles off Langebaan this week — possibly the first time such an event has been witnessed in local waters.
About 20 orcas ripped into a large group of about 1,000 seals in a five-hour feeding frenzy documented by foreign tourists on an ocean safari led by local boat operator Rainer Schimpf.
The sighting is unusual in that killer whales prefer other prey, including dolphins and sharks, though autopsies have found seal flesh in orca stomachs.
The encounter on Tuesday could have widespread implications due to the prevalence of rabies in the local seal population and concerns that the disease could spread further afield.
The seals, clearly in a state of panic, leaped frantically out of the water, attempting to escape
— Rainer Schimpf, owner of Atlantic Ocean Safaris in Langebaan
“The orcas had encircled the [seals], moving counterclockwise to form a bait ball of seal meat, tightly compacting the animals into a dense formation,” Schimpf, owner of Atlantic Ocean Safaris in Langebaan, told the Sunday Times.
“The scene was breathtaking: about 20 orcas worked in co-ordinated precision, tightening the circle while continuously surrounding the seals from all sides at all times, until the seal bait ball had a diameter of roughly 100m.
“Orcas would split out of formation suddenly and attack from two sides at the same time,” said Schimpf.
“The seals, clearly in a state of panic, leapt frantically out of the water, attempting to escape. But the orcas tricked them again and again — a small number of orcas would pretend not to be interested and swim by, while another group of orcas came from the side or below, targeting the seals.
“Sometimes the orcas would use their tails to hit and injure the seals, then move in and finalise the hunt,” Schimpf said.
The seal massacre adds a new twist to a series of orca attacks on whales and sharks recorded off the South African coast in recent years. Local research group Sea Search, which is linked to Stellenbosch University, is leading a long-term study into the killer whale behaviour.
Sea Search co-director Simon Elwen said killer whales did not normally prey on seals, probably because “seals are small, agile and tricky to catch — maybe not worth the effort”.
“But killer whales do change behaviour and learn new techniques, and maybe they are opening a new door [by eating seals].”
He said a pod of killer whales appeared to be currently targeting a supergroup of humpback whales, with another documented attack this week.
Schimpf last month photographed a killer whale attack on a humpback off St Helena Bay.
He expressed concern about the possibility of orcas becoming vectors for rabies.
“A relevant question now will be, if seals really suffer from rabies, and are now taken by orcas, where will rabies be taken too?” he said.
“Orcas feed on all marine animals and mammals like whales, dolphins, and they swim across all oceans.”
Local authorities last year issued several warnings about confirmed cases of rabies in seals, amid a rise in the number of seal attacks on people and dogs on beaches.
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