Well there is far more than 2x times the water, most of which can't be walked on or isn't walked on...are you implying there is higher density in the bow than the lower elbow?
I would argue that the regulations already imply where the most vulnerable spawning habitat is. Generally, there is a method to the madness.
That being said, there is Way too much huff and puff about the bow. It's been a remarkable fishery for decades and this year put up one of the best big fish years in memory. If a river running through the middle of a major city can do that, It'll be okay. Really. If you have to sweat anything, worry about water usage, low flows, waste and pollution.
There should be more threads on vulnerable wild fisheries of bulls and cutthroat that have assholes poaching, quading in and logging/mining the headwaters. Don't get me wrong, I love the bow, but Native fish are much more of a concern as they've been in decline.