Juvenile outmigration is an important life stage for Yukon River Chinook salmon. Recent research suggests that much of the variability in Chinook salmon production may occur prior to the first summer at sea (Howard et al. 2016, Murphy et al. 2017) and that larger fish with higher energy content at the end of their first marine summer had a greater chance of surviving to adulthood (Howard et al. 2016). Outmigration from the river to the marine environment is physiologically stressful. Larger in-river has been linked to both downstream survival (Zabel & Achord 2004) and adult returns (Zabel & Williams 2002, Woodson et al. 2013) in wild Chinook populations, and suggests that early growth in fresh water may be an important indicator of later growth (Ruggerone at al. 2009). This is consistent with an emerging idea that fish need to prepare themselves for life history transitions such as smolting or offshore migrations. This preparation is associated with increased energy reserves, which are maximized by increased size.
The objectives of this project are to quantify outmigration timing from ice out through the end of the August, examine size (length and weight), growth, diet, energetic condition, and smolting stage of outmigrating juveniles in relation to environmental variables in the freshwater and nearshore marine environment, and to collect genetic samples to assess outmigrant origin.