Another aspect of survivability I've wondered about is time of day that the salmon move once they're back in the river. I wonder if some are predisposed to mostly swim during the day and some predisposed to move at night.
I've noticed that there seems to be a good number of Coho reach the hatchery over night, and that there seem to be more difficult to catch during the day.
If we're continuing to harvest day-swimmers in the river, and a higher percentage of night-swimmers are getting to spawn, we are likely interfering with that aspect mix in the local Coho populations.
Somewhat along the lines of what the hatchery concluded about Steelhead and time of year they return.
There was a good article posted a few years back about Kanaka creek coho and their spawning habits. During the day they hide in deep pools or under banks and then in the night they would migrate into tributaries less then a food deep and spawn.
I would imagine they do this to avoid Dufus!