Estuaries provide rearing habitat for some juvenile ocean type Chinook Salmon. To gauge the importance of this habitat and characterize its use in the Skagit River, we calculated the respective percentages of juvenile and adult populations represented by juvenile life history patterns in both a large and a small brood year. We identified delta rearing life histories based on otolith check patterns corresponding to specific habitats within the tidal delta, finding that more fish bypassed the estuary (fry migrants) in a large brood year, and that most tidal delta users followed a straightforward pattern of stepwise increases in growth rate culminating in fast growth in Skagit Bay at time of capture. Fish leaving the estuary after a longer rearing period were larger and grew faster in the bay. Fry migrant life histories were poorly represented, if at all, in adult Chinook Salmon returns. From these results we suggest that large brood years exceed the Skagit estuary’s rearing carrying capacity and that adult returns benefit from the survival advantage likely conferred by the size increases of tidal delta rearing.
