Haida Gwai Shark Schooling

Surprisingly, no one has really understood the extent of the shark interception of the salmon migration path and this is a major revelation.  We do not know the details but it could well be a major cause of salmon population volatility over the decades.

This past year we had a major return of sockeye following years of devastated returns.  The interception can best explain the sharp swings were every other explanation is clearly wanting and unconvincing.  Here we are seeing enough sharks to be convincing.

The shark population may well also need strong harvesting pressure to relieve pressure on the salmon.

Shark week: Marine biologists hit ‘hot spot’ off B.C. coast

MARK HUME  

VANCOUVER— From Monday's Globe and Mail

Published Sunday, May. 08, 2011 10:07PM EDT

When the group of volunteers set out, following a zigzag course along the coast of British Columbia, they never expected to sail into shark-infested waters.

But midway through their cetacean survey between Washington and Alaska, there was no doubt about what they were seeing. All around the boat, which had steadily been working its way north at about nine knots, the dorsal fins of sharks could be seen slicing the surface.

“All of a sudden, it was shark, shark, shark every few seconds,” Dr. Rob Williams said. “It was obvious we’d hit a huge hot spot.”

It has long been known that salmon sharks and blue sharks visit B.C. waters. Dead ones wash ashore now and then and fishermen sometimes bring them up thrashing in trawl nets.

But it wasn’t until Dr. Williams and his associates surveyed the coast a few years ago that anyone realized a huge population of sharks gathers in the late summer, just south of Haida Gwaii, in Queen Charlotte Sound.

It makes you wonder what else might be out there.

Dr. Williams, a research fellow at the University of St. Andrews in Scotland, made the shark discovery while conducting a marine mammal survey with the Raincoast Conservation Foundation, which is concerned about the potential impact of oil and gas development on the West Coast.

Using a 21-metre Raincoast research vessel, they set off to survey the near shore waters to get abundance estimates for seven key species: harbour porpoise, Dall’s porpoise, Pacific white-sided dolphin, humpback whale, fin whale, common minke whale and northern resident killer whale.

Then they ran into the sharks – and made one of the most remarkable marine findings in many years. In a paper published last year, and tabled last week with the Cohen Commission in Vancouver, Dr. Williams states an estimated 20,000 blue and salmon sharks gather in a relatively small area each summer. How long they are there and why isn’t known, but sharks are driven by hunger, so it’s a good guess they are there to feed.

“Explanations for this concentration of sharks include foraging, resting and reproduction,” Dr. Williams states in his paper. “These sharks may concentrate in this area during July and August to intercept adult salmon on their return migration from the North Pacific Ocean to natal streams in the region. For instance, salmon returning to the Fraser River – the largest of Canadian salmon runs – use this more northerly route through Queen Charlotte Sound and Johnstone Strait during times of higher-than-normal sea temperatures.”

Dr. Williams said because they were doing an abundance survey, the team didn’t stop to catch sharks to look at stomach contents. That would have told them if the sharks were indeed feeding on salmon, or on the northern elephant seals, Pacific white sided dolphins and ocean sunfish that also concentrate in the area.

“I would love to go back there and tag some sharks, take some stomach samples, and even put critter cameras on some to see what they are up to,” he said in an interview from Scotland.

“And who knows what else we might find out there.”

Indeed. One has to ask, if 20,000 sharks were overlooked until now, what else is going on out there that we don’t know about?

Dr. Williams said his research was restricted to the sheltered inshore waters east of Haida Gwaii and Vancouver Island because the vessel he had wasn’t built to go far offshore. Funding was also limited, and it all came from private sources.

He wants to return to the West Coast, to spend more time in the shark hot spot and to venture farther out, where he’s convinced there are more surprising discoveries just waiting to be made.

“The seaward extent [of the aggregation zone] is completely unknown,” he said. “I would love to go out there, but you can’t rely on the kindness of non-profits to go out 50 to 60 kilometres offshore.”

In other words, he needs a bigger boat and more funding.

There are two reasons the government should support him. First, if you don’t know what you’ve got, you can’t protect it. And second, the idea of a B.C. shark cam is just too cool to pass up.