The reason I ask that is because there was a recent article on the survival rates of some of the salmon out of the Chilko system in B.C. When they have huge numbers migrating at once, they have a far better survival rate. I think that's roughly 90% versus 40% if they have low numbers.
We can assume that correlates to the fact there's still the same number of predators out there that would take the same gross number out, but that percentage in a smaller group would be much higher.