The most surprising thing about the kill was how easy and fast it was.
The seal dived into the black depths of the canyon pool in the Pitt River, flushed out a spring salmon, trailed it across the shallows and pinned the fish against a rock, killing it with a violent head jerk.
The chase had taken less than a minute and had we not been rafting by at that moment, it would have gone unseen - as perhaps tens of millions of such kills do each year.
It's not known how many salmon are killed by seals and sea lions in British Columbia annually, but a few years ago Peter Olesiuk, of the Department of Fisheries and Oceans, did a study of harbour seals in the Puntledge River, on Vancouver Island.
He concluded that three dozen seals had killed 10,000 adult chum salmon in the fall spawning run.
Find the number shocking?
Well, consider this: Mr. Olesiuk also calculated how many salmon fry the seals were eating in the spring: 3.1 million.
"They take 60 to 70 chum fry, per minute, per seal," he says. "They eat the young fish like popcorn."
Mr. Olesiuk points out that the Puntledge is unusual because it runs under a well-lit highway bridge that allows the seals to feed at night. But the efficiency with which seals vacuum up salmon should concern everyone.
Mr. Olesiuk's latest coast-wide census, to be released this week, shows B.C.'s seal and sea lion populations are at historic high levels.
There are an estimated 105,000 harbour seals on the coast - up from about 10,000 in the early 1970s - and 28,000 Steller's sea lions, the highest number since the early 1900s.
Both seals and sea lions used to be hunted on the West Coast, but there has been no commercial harvest or predator control efforts since 1970.
By contrast, on the East Coast, the commercial hunt this year will take 330,000 from an estimated overall population of seven million.
In B.C., salmon farmers have permits to kill seals and sea lions that invade their pens. But the take of a few hundred is relatively small.
It isn't known how many seals and sea lions are killed illegally, but sports, native and commercial fishermen do shoot some.
"You do find a carcass washed up now and then with a bullet hole in it, but I suspect a very small number of animals are killed this way," Mr. Olesiuk said.
On the Fraser River, the Sto:lo Tribal Council has repeatedly asked for permits so fishermen can legally shoot seals and sea lions. So far those permits have been denied. As a result, a clandestine seal kill is taking place.
"Seals will come right into our nets and rip the salmon out," said Ernie Crey, a Sto:lo fisheries advisor. "And I can tell you that fishermen do pull out their guns and deal with it … I can't understand why a salmon farmer can get a permit to protect his salmon, while native fishermen can't."
Fishermen on the Fraser say it used to be unusual to see seals far up the river, but now they are everywhere.
Pitt River Lodge owner Danny Gerak says there are 15 seals at the river mouth this spring, and last summer, during the height of the salmon run, he counted 180 hauled out on log booms.
He favours a seal cull, but added: "It's pointless to kill seals if you don't address the other problems, too. I think salmon farms and hydro projects do more damage."
But removing seals from rivers can have immediate and direct impact.
In Scotland, a study found that taking a single seal out of the Moriston River increased the sports salmon catch by 17 per cent. On other rivers, removing seals had varying results, with salmon catches increasing from less than 1 per cent to more than 33 per cent.
Mr. Olesiuk says that on big rivers, when salmon are abundant, seals do minimal damage. But in some places - especially where salmon runs are small - they can be devastating.
Twelve years ago, there was a temporary seal cull on the Puntledge. The salmon run flourished afterward and people are now calling for another kill.
Mr. Olesiuk urges a cautious approach, saying site-specific scientific study should precede any cull.
But with B.C. salmon runs at historic lows and seal populations at historic highs, it is obvious action needs to be taken.
Mark Hume