In 2015, adult spring Chinook returns to Bonneville Dam were the fourth highest on record. (Counts go back to 1938, averaging less than 100,000 per year.The highest 4 returns have all been in the past 15 years.)
Adult fish returning from the ocean to their spawning grounds pass the dams through fish ladders. Snake River chinook and steelhead go through 8 dams (Bonneville to Lower Granite) and Upper Columbia chinook and steelhead go through 4 federal dams (Bonneville to McNary). Upper Columbia stocks also go through public utility-owned dams above McNary. See route here.
The FCRPS BiOp sets adult fish survival standards for each interior Columbia Basin ESA-listed species. Survival estimates (shown in the chart above) are designed to isolate the effects of dam passage from harvest-related mortality and straying, but unreported harvest and inaccurate stray rates still affect these estimates.
For 2013 (the most recent year for which we have estimates) three stocks surpassed the BiOp performance standard and two were below it. In 2013, the Corps initiated a two-year adult passage study to better understand and quantify the losses.
Lower Monumental Dam John Day Dam
The Dalles Dam McNary Dam