MT,
I hope to never have to find out firsthand what knife techniques would prove the most effective.

What's clear to me is that if that field biologist hadn't had the foresight to carry that bear spray, the end might of been far different ( for him).

Predatory bears must be a concern regardless of the long odds, or the people who work daily in the field wouldn't carry bear spray or firearms (sometimes both).

In a large group, say 4 or more, you could probably drive off a predatory bear by sheer force of numbers, but a solo paddler or even a couple if one is attacked and crippled/killed in the intial attack has the odds against them unless they have a option other than going one on one against a bear.

I've driven for over 50+ years now, never been in an accident. Never had to rely on my seat belt, but I've always worn them, even when it wasn't the law to do so.
Small price to pay for the knowledge that if the worst scenario happens, I have a fighting chance to survive.

I look a Bear Spray the same way. I don't care how unlikely the chance's are to be attacked by a wild critter, that's little comfort when your the one the odds fall on. :'(