I think another factor is cultural.  I caught a whitefish in Pickerel Lake once...looked like a rough fish, almost like a carp.  

I didn't know what it was until I got home and had a fisheries biologist id it.  Anyway, I let it go, but found out it is considered a delicacy.  

Carp, for that matter, are eaten by millions of people!  

So to me it's: fish feed, water quality, and culture.

prouboy