There are some indications that larger fish at smolting time subsequently suffer less mortality at sea than smaller fish. One of the 'solutions' some fish have evolved is to hold territories, or areas from which they chase other fish. Since they use these territories for the sole purpose of feeding, it is called feeding territoriality. Feeding territoriality appears to be a feeding tactic adopted by many juvenile stream salmonids, be it coho, chinook salmon, rainbow trout, etc. Many territorial fish are larger, and therefore probably grow faster, than their non-territorial counterparts of the same age.
Most young salmon are cryptic, in that that they blend with the bottom.
In moving, they become more visible to predators. The fun part for scientists is to figure out how young salmon should behave when. If our understanding of the system is indeed correct, then a simple rule of thumb for non-reproductive animals is to minimize the ratio of mortality rate over growth rate, i.e., for a given food, to risk as little as possible. This rule, although it sounds simple, has been arrived at after many complicated calculations. However, another side of the coin is that if faced between two bits of food, one large and the other small, the fish should take more risk to acquire the large one, since in eating the larger bit it may grow more.