Sacramento River Steelhead Trout: Survival of Wild and Hatchery Smolts

There is a general lack of knowledge concerning the survival and behaviors of juvenile hatchery and wild steelhead trout (Oncorhynchus mykiss) in the Central Valley. The objective of our study is to examine both hatchery and wild juveniles to elicit differences in movement and success rates, route selection and behavior. Vemco V7 acoustic tags were implanted in hatchery and wild steelhead smolts in order to monitor their survival and behavior with mark recapture data in the Sacramento River, San Francisco Bay Estuary, and the coastal ocean from 2008-2010.  Hatchery fish were released at three locations (Jelly‘s Ferry RKM 517, Irvine Finch RKM 414, and Butte City RKM 363) in December and January of each year while wild fish were captured and tagged from a rotary screw trap located on Mill Creek (RKM 462).   Hatchery fish showed a pattern of holding prior to exiting the system.  There was high loss of tagged fish immediately following the release of hatchery individuals across year and release groups.  A similar decline was seen for wild fish, however, the magnitude of the decline was significantly smaller.   Route selection varied between years as well as between hatchery and wild fish.  Fish chose the mainstem Sacramento River and Georgiana Slough in the highest proportions during both years while western routes were utilized to a lesser degree.  Survival of wild fish was higher than that of hatchery fish.   There was considerable variation between the timing of wild and hatchery fish successfully migrating to the ocean.  Hatchery fish were found to migrate over a larger time window and had considerably higher variation in their migratory rates than wild fish.   Furthermore, there was variation in movement rates between years for hatchery fish.   During 2009 hatchery fish that reached the Golden Gate Bridge (RKM 0) had an average migratory time of 20 (13-36) days if they were released in December, 23 (10-57) days if they were released in January, and 12 (10-15) days if they were wild smolts.  In 2010 hatchery fish that reached Golden Gate had an average migratory time of 10 days (8-19) days and 17 (13-21) days, while wild fish took an average of 9 (5-14) days to exit the system.