Life History Strategies of Coweeman Fall Chinook, with Emphasis on Residency and Growth in the Columbia River Estuary, As Inferred from Otolith Microchemistry

Growing evidence in the Columbia River estuary suggests juvenile Chinook salmon (Oncorhynchus tshawytscha), utilize portions of both the freshwater and salt water components of the estuary before out migration.  However a clear link between these estuarine using juvenile life history strategies and returning adult populations has not been made. To test the hypothesis that estuary rearing juveniles contribute to adult populations, we chemically marked outmigrating wild juvenile Chinook salmon at the Coweeman River smolt trap and collected retuning adult otoliths from the spawning grounds on subsequent return years. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) was used to analyze chemical patterns in otoliths.  Otolith microchemistry was used to estimate the size and timing of juvenile outmigration.  Furthermore residency within the freshwater portion of the estuary was estimated based on recoveries of chemically marked adult otoliths from the Coweeman River.