I have to agree with carcassman - Food availability rarely receives enough attnetion in these discussions. For stream rearing species, food availability is often limiting production during the summer months, particularly in small streams. Density dependent growth is clearly evident - lower density results in larger fish. Higher density results in smaller fish. Food availability is limiting the total biomass in the stream. See Quinn's book for a good discussion of this. So when people say that the capacity of our streams is a fraction of what might have been the case historically, that isn't necessarily due only to poor spawning success or lack of quality rearing space. Without sufficient food resources, production will suffer.

I participated in an experiment 20 years ago where food was artificially increased in a small coho stream. Growth and density both increased dramatically where food was supplimented, resulting in as much as an 8-fold increase in coho biomass. Carcass/nutrient supplementation studies have shown a similar response with no change in the physical habitat. Both food production and rearing space are critical components of freshwater rearing habitat.