Migratory Behavior and Estimated Parr-to-Smolt Survival Rates of Wild Snake River Spring-Summer Chinook Salmon from the Salmon River Basin, Idaho--Have Things Changed over the Last Two Decades?

Survival and juvenile migration timing are key life history traits for at-risk salmon populations.  To estimate these traits in threatened wild Snake River spring-summer Chinook salmon, each summer we passive integrated transponder (PIT) tagged fish as parr in 3-17 natal streams of the Salmon River basin per year from 1988 to 2009.  Each following spring, fish were detected as smolts in the juvenile fish bypass systems of the lower Snake River dams.  Estimated parr-to-smolt survival to Lower Granite Dam (1993-2010) ranged from 3 to 48% for individual populations and from 8 to 25% annually (annual average = 16%) for all streams combined.  Timing of the 10^th to 90^th percentile passing the dam ranged from 22 to 55 days for the combined wild populations (average 38 days) from mid-April to mid-June.  Although the 10 and 50% passage trends have changed little, the 90% passage trend has shifted 12 days earlier over the years for these wild fish.  Currently we are exploring factors that may be related to this earlier 90% passage and shorter middle-80% passage time for all wild fish at the dam.  Long-term water quality monitoring and survival/timing data for parr and smolts and their observed life history strategies are discussed with respect to climate change.