The Nisqually Delta Restoration is the largest estuarine restoration project in the Pacific Northwest, USA. In 2009, 8 km of earthen dike was removed, resulting in the addition of over 440,000 m2 of tidal channel habitat in South Puget Sound. Various success criteria have been proposed for assessing restoration trajectories, but in the context of salmonid rearing, success is best evaluated based on whether outmigrating juvenile salmon can access and benefit from suitable estuary habitat. We integrated three years of post-restoration monitoring data including habitat availability, invertebrate prey biomass, and juvenile Chinook salmon (Oncorhynchus tshawytscha) body condition and growth. Our objective was to determine whether juvenile Chinook were using the restoration area, and if they were benefiting from local invertebrate prey communities.
Our analyses demonstrated that the development of a complex network of tidal channels and a resurgence in dipteran biomass resulted in up to 6 million kJ of added invertebrate prey productivity. This led to a notable shift in prey preference within the restoration area, whereby Chinook switched from eating primarily amphipods to flies. Body condition across tidal marsh sites was positively influenced by energy availability, regardless of dietary composition. Furthermore, even though recent entrants were captured in higher densities at sites closer to the Nisqually River mainstem, we did not observe density dependent effects on body condition at these high-energy sites. These findings have implications for the management of Puget Sound Chinook, since hatchery release has the potential to put competitive pressure on natural-origin populations during the outmigration season.