Sharks and chum? On the trading in momentum stocks by various investor types

Controlling for the trading activity of more and less sophisticated investors ("sharks" and "chum"), past returns alone no longer predict that future returns will move in the same direction. I.e. momentum seems to be generated through the trading activity of these two groups. I nd that past and current buying pressure of sharks positively relate to current returns; past and current selling pressure from chum positively relate to current returns. This is consistent with sharks being simply better able to identify good investment objects at any point in time; chum naivly go in the opposite direction.