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Salmon Redd Counts

1948 - ongoing,   Dr. Dennis D. Dauble

The salmon in the Hanford Reach area are classified as the upriver bright (URB) race of fall Chinook salmon (Oncorhynchus tshawytscha). Fall Chinook salmon migrate upstream to spawning areas in the Hanford Reach from mid-August through October, they dig redds and deposit eggs from late October to late November. (Dauble, D.D., and D.G. Watson. 1990. Spawning and Abundance of Fall Chinook Salmon (Oncorhynchus tshawytscha) in the Hanford Reach of the Columbia River, 1948-1988. PNL-7289. Battelle, Pacific Northwest Laboratory, Richland Washington.) The Hanford Reach is a 90-km segment of the Columbia River extending from the upper end of McNary Dam Reservoir (near the downstream border of the Hanford Site) to Priest Rapids Dam.

Aerial counts of Chinook salmon redds have been conducted annually at Hanford since 1948 using fixed-wing aircraft. One to seven surveys are flown each year at approximately weekly intervals from late September to November. Estimates for the number of redds are made at altitudes of 244 to 366 m (800 to 1200 ft) and at air speeds of 120 to 161 km (75 to 100 miles per hour). When the salmon redds are widely spaced, they are enumerated individually. When the redds are close together or overlap, they are estimated in units of 10 or 50. Two or more counts are made of areas of heavy spawning for each survey. When possible, estimates of the number of redds were compared between observers. Counts were usually obtained near mid-day with the sun at the observer's back, and polarized glasses were sometimes worn to reduce glare.

Newly excavated redds appear as light-colored, regularly shaped circular or oval areas that contrast with the normally darker periphyton-covered substrate. The redds remain visible for about 6 weeks before their surface becomes recolonized by algae growth. For this reason, some redds counted at the beginning of the spawning period may not be visible by the end.

Redd data consists of totals for 10 designated areas within the Hanford Reach for each survey date. Data outside these areas are included in the "other" column. Most of the "other" redds reported since 1980 are located at China Bar, a man-made shoal constructed near river km 628.

A yearly redd total is calculated using peak counts within designated areas. Peak spawning is defined as the date with the highest total redd count. The date of peak spawning differs among areas.

For more information on this study and others, please go to the Ecological Monitoring and Compliance Project website.