Bottom-up processes mechanistically link with top-down control of populations, and these interactions are mediated by environmental variability and human-induced changes in land and water use. Size-selective mortality can be a significant force regulating recruitment of salmon and may be imposed at different life stages and habitats for different species, stocks, or life history types. The first months of marine growth are commonly regarded as a critical period for growth and survival of salmon. For ESA-listed Puget Sound Chinook salmon, emergent bottom-up patterns include: 1) a critical growth period occurs when body mass increases 2-4 fold during the first month of feeding in epi-pelagic habitats within Puget Sound; 2) that growth is limited primarily by food supply, but can be exacerbated by warm temperatures in shoreline habitiats; 3) higher growth and survival correspond with higher contributions of key prey like larval crab. Piscivorous fishes exhibit size-selective predation on juvenile salmon in Puget Sound, and resident forms of Chinook salmon are capable of imposing significant mortality on subyearling Chinook in Puget Sound
