I don't know much about green sunfish, but it sounds like he is doing exactly what you think he is... eating the shiners. Might just be smart enough to 'herd' them into an easy spot to catch or into the open.
I love shiners, did I mention that? What I have in particular is Bridle Shiners,
Bridle Shiner Noticed another fresh 'spawn' of the little critters last night, and the half dozen I put into a drainage ditch on my property just to eat some of the mosquito larvae have turned into thousands of 1-2 inchers... shame the water is drying up faster then I can scoop them out. As far as being quick enough/smart enough to avoid easy predation... seems they get better with age/size... the real small ones are easy pickings and don't flee from anything but the larger ones seem to.... and they would be the breeders.
On another note about sunfish... I can't purchase them here so I have been catching them from a local waterway... what I am catching seems to be either a cross between a bluegill and a pumpkinseed or a redear and a pumpkinseed... is this common? (Just because they look just like a pumpkinseed except lacking the blue 'striping' and some have a red tab on the gill flap.
