The Use of Otolith Microstructure to Examine Estuarine Utilization and Life History Diversity of Juvenile Chinook Salmon As Related to Restoration Efforts on the Nisqually River

The Nisqually Fall Chinook salmon population is one of 27 stocks in the Puget Sound evolutionary significant unit (ESU) listed as threatened under the Endangered Species Act (ESA).  Preservation and extensive restoration of the Nisqually delta ecosystem is currently taking place to assist in recovery of the stock as juvenile Fall Chinook salmon are dependent upon the estuary.  Furthermore, a Chinook salmon recovery priority of the Nisqually Tribe is to develop a self-sustaining, naturally spawning population.  Currently, this population consists of offspring from both hatchery and natural spawners.  A pre-restoration baseline that includes characterization of life history types, estuary residence times, growth rates, and habitat use is needed to evaluate the potential response of hatchery and natural origin Chinook salmon to restoration efforts and to determine restoration success.  Otolith analysis was selected as a means to examine Chinook salmon life history, growth, and residence in the Nisqually Estuary.   We will report on differential usage of the estuary by natural and hatchery reared juvenile Chinook salmon and their expression of life history diversity during mid-recovery of the population.