Evaluation of Juvenile Salmonid Outmigration and Survival in the Lower Umatilla River Basin, Annual Report 1998-1999.

Evaluation of Juvenile Salmonid Outmigration and Survival in the Lower Umatilla River Basin, Annual Report 2001-2002.

“…Hatchery summer steelhead released lower in the river displayed improved emigration success and migrant survival over upper river releases. This was consistent with previous trends (Ehlers et al 2001, Knapp et al 2002, and White et al 2003. In addition, first year monitoring of large-grade steelhead released from the Pendleton Acclimation facility revealed an increased rate of detection and higher emigration success than fish from any other release group.…”

“…In addition, April released fish were released during spring freshet, where flows reached a high of almost 5,000 cfs. Flows have not fluctuated this drastically since the 1997 migration year (Ehlers et al 2001, Knapp et al 1998b, and White et al 2003. Furthermore, trap efficiencies for yearling fall chinook salmon in 2002 were roughly 20% in March but dropped to 1.5% during the April release.…”

“…Current and past reports have indicated that relationships between environmental variables and emigration timing of juvenile salmonids in the Umatilla River are species specific and variable from year to year (Ehlers et al 2001;Knapp et al 1996Knapp et al , 1998aKnapp et al , 1998bKnapp et al , 2000Knapp et al , and 2002White et al 2003). The high variability in these relationships is likely due to seasonal variation in natural and augmented river flows, water temperature, and hatchery fish release sites, dates, and size.…”

“…Little change was seen in migration parameters of hatchery or natural salmonids in 2002 compared with previous years. However, detection data of hatchery salmonids from 1999 -2002 has provided valuable information on emigration success of juvenile migrants and monitoring of migration trends (Ehlers et al 2001, Knapp et al 2002, and White et al 2003.…”

“…Several years of fork length data and two years of PIT tag data has indicated a prolonged residency for hatchery coho salmon, in which they are actively feeding (increased monthly mean fork length during the monitoring period) and potentially competing with naturally rearing juvenile salmonids (Ehlers 2001;Knapp et al 2000 andWhite et al 2003). Ideally, hatchery smolts should only utilize the Umatilla River as an emigration corridor to the sea.…”