Sunshine pleco question

I have had this pleco for about 3 months. I have not seen it eat once, but it is still alive so i imagine it has to be eating right? I leave shrimp on the bottom of the tank every night after i turn the lights out, but i have no idea if he is eating (my other fish like them too). Lately the shrimp have only been about 1/3 gone, so i am concerned that if it was eating it isnt now. Is there any way to find out?
Fish is about 6" long.

With Plecos, I generally just leave food and forget about them..lol. I have never lost one, in fact, I have an extra BN right now that I have no idea where it came from.

Plecos eat when they want to. I rarely give anything extra to my plecos. There is plenty of food that my Cichlids spit out, that the plecos can eat. Plus they have the algae, wood, and other things to munch on. Every once in a while I will drop in a few algae wafers or bottom feeder wafers.

I rarely see my pleco eat but when I gravel vac I can tell he has been finding something since there is so much pleco poop! I give an occasional couple algae wafers but mostly rely on him to scavenge his food.