From what I have noticed it is the depth at which they spawn. Large mouth tend to be really shallow when they spawn (2' - 4'). Small mouth beds are deep as 15' sometimes. I'm no to sure on the walleyes but I think they are deeper spawners than Largemouth.

Some times it just depends on the structure or bottom texture. They all need a gravely rocky bottom to spawn. Back east the largemoutn females would swim back and forth over one spot to move the sand and silt away to expose the rocks. I've seen them do this in a couple of Idaho lakes too.