You probably are don't hear much about them from biologists because for the most part they are considered unwanted trash fish with anglers paying little interest in them. Keep in mind, carp are for the most part of fusiform fish with no large spines. In other words, they're easy to swallow. Smaller carp stay in the thickness of aquatic vegetation out of sight of both human eyes and predatory eyes.

Common spawn over aquatic vegation, generally in shallow backwater areas. I have never heard of them migrating up rivers to spawn. Grass carp require fast moving water to successfully spawn and few rivers meet their requirements. Even if diploid grass carp were present, most river systems would not meet their spawning needs.