It looks like an aquatic Isopod. Have seen a lot of brackish ones on the rocks around here at night coming out the water, I assume to feed. I would bet trout feed on them and could be a food they target at dusk and dawn when they start moving to shallow water, if they do. Either way trout likely feed on them at some time or another. Looks like the alder pine cones that I find in a lot of trout locally.