I suspect that RES move up shallow to feed every night once the sun goes down. If I am right there should be very significant differences in the capture rates of RES by electroshocking during the day vs. electroshocking after sunset.
The ones I have caught in shallow water were around sunset or at least when the sun was very low in the sky and the lighting was getting subdued.
Your observation would seem to make sense in relation to snails. I don't know how many snails reside deep, but the high numbers I have seen are along the shore line on the fresh algae on the rocks or plants. It would seem the RES would want to move up into this shallow water at some time during the day to take advantage of these snails.
I do know the snails move deeper and under the rocks more than on top of them as the water cools, but my visible snail population is way down this fall compared to what it was last fall when I added an additional 125 3" RES to my main pond. The ones of those fish I have caught are in the 6-7" range now and I think they have worked on the snails a bunch this year.
