Orcas chow down sharks

VANCOUVER ISLAND (CANADA)- Scientist John Ford with the Department of Fisheries and Oceans of Canada didn’t know what he saw at first. Hyperventilating orcas, a wild feeding frenzy and chunks of oily meat floating on the sea. The orcas of the coast of Vancouver Island weren’t feeding on salmon of sea lions. No they were having a feast of shark meat! On the Canadian West Coast the top predator in the ocean is not the shark, it’s the orca.

Ford, a research scientist, was aboard a boat north of Haida Gwaii but just south of Alaska, studying the feeding habits of a little-known group of offshore killer whales. The mammals were hyperventilating, arching their backs and diving deep. On the hydrophone, Ford could hear their excited songs.

Minutes passed and then a chunk of tissue — about 250 grams in size and later proven to be part of a liver — floated to the surface, coming to rest in a slick of oil. More and more tissue and oil soon appeared, covering an area of ocean in a sheen hundreds of metres in size and flattening the water’s ripples. Ford and a colleague collected samples, which were later analyzed at DFO’s Pacific Biological Station in Nanaimo, British Columbia.

Hypothesis
The tests confirmed Ford’s long-held hypothesis: the offshore orcas weren’t eating salmon or sea lions. They were chowing down on sharks, specifically sleeper sharks. The sleeper shark is one of 14 shark species found in British Columbian waters. Blackish brown or slate green in colour, the shark can grow to 4.3 metres in length.

“It was one of the top days in my 30-plus-year career studying wild killer whales,” said Ford, of watching the feeding frenzy. “It was the culmination of many years of speculation, debate, you know, pondering about what it is that these animals feed on. “It was really gratifying to see that this piece of the jig-saw puzzle finally fell into place.”

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