Lake Level Effects on Shoreline Spawning Lost River Suckers (Deltistes luxatus) Estimated from Passive PIT Tag Detections

One of the last remaining populations of the endangered Lost River sucker spawns along the eastern shore of Upper Klamath Lake.  This lake is managed to balance water needs of irrigators and the federally listed fishes that inhabit the lake and the Klamath River. As a result of water withdrawals in 2009 and insufficient over-winter recharge, lake levels during the Lost River sucker spawning season of 2010 was the lowest since 1974. Individual PIT-tagged suckers were passively detected at shoreline spawning areas during the across 8 years (2006-2013). We compared movement among spawning areas, metrics of skipped spawning, and spawning duration with contrasting water levels. Few individuals strayed from shoreline spawning areas to other known spawning locations in lake tributaries. During the extreme low water year of 2010, 14% fewer female and 8% fewer male suckers joined the shoreline spawning aggregation than in the other years. Suckers visited fewer spawning areas within Upper Klamath Lake in 2010 than in other years, and the median duration fish spent at spawning areas in 2010 was at least 36% shorter for females and 20% shorter for males relative to other years. We identify lake-surface elevations, above which spawning is unlikely to be effected.