Sharks: Policing the community?

#1
As some of you may have known, I was having a bit of a problem with my Rosey Barbs bothering my angels. I had the issue of not wanting to take either of them back, and had nowhere to put either species to seperate them. To further complicate things, I have been having a helluva time finding a partition for my 75g in my LFS locales.

Anyways...I was keeping an eye on things yesterday, and I noticed the barbs were teaming up, chasing the bigger angel around. I had finally had enough, and decided to take the barbs back. I was just about to get a bucket, when my black shark AND Irridescent Shark (who, by the way, is almost over his bout of 'Ick') came out of nowhere and chased off the barbs...and have pretty much been doing that ever since. They don't chase them around...they just keep them away from the angels.

I'm just wondering if this is 'normal' behaviour for sharks, or if this has happened for anyone else.