Spawning surveys are conducted on the mainstem of the Okanogan River and all of its tributaries that contain sufficient water to support spawning. The process begins with two surveyors on pontoon boats floating down the mainstem Okanogan River searching for redds, shallow pits in the gravel substrate of a stream where salmon and steelhead lay their eggs. When redds are discovered, the depth of the redd is measured, the location is marked with a GPS point, and the redd is flagged along the bank to prevent double-counting. The smaller size of the tributaries precludes the use of pontoon boats so two individuals walk in or along the stream while searching for redds, beginning at the mouth of the creek and proceeding upstream.
The mainstem and tributaries are surveyed three times during the steelhead spawning timeframe that begins in late March and ends in early May. If spring runoff causes a dramatic increase in river discharge, increased turbidity can make observing redds difficult. If this occurs (typically around mid-April during the second round of observations), redd numbers may be estimated by using the number of redds observed on the first and last round as well as the number of fish observed passing Wells Dam downstream.
Once the total number of redds is tallied, a calculation used by the Washington Department of Fish and Wildlife is used to estimate total spawning escapement to the Okanogan Basin. Sex ratios are calculated from adult traps on Omak, Bonaparte, and Antoine Creeks and sampling at Wells Dam. This ratio is then used to expand the number of redds observed into the likely number of fish per redd. Assuming each female will only produce one redd, an observed sex ratio of 1.5:1.0 males to females would be expanded to 2.5 fish per redd. Applying the sex ratio multiplier to the total number of redds allows us to estimate total spawning escapement.
During spawning, the redd is excavated by the female when she turns on her side and fans the gravel with her tail. The moving water washes the substrate downstream, allowing the female fish to lay her eggs in the remaining depression. Once the male fertilizes the eggs, the female covers the eggs by fanning the substrate upstream of the redd so it will wash down and cover the eggs. This leaves a distinguishable pit with a mound on the downstream end (the tailspill). Additionally, the periphyton is removed from the disturbed substrate, making the redd distinguishable from the surrounding substrate which is still covered in periphyton.
Beginning in 2012, aerial redd surveys will be conducted to determine if this method could augment or even replace efforts on the ground. An expert in aerial surveys will fly with OBMEP staff to determine if aerial steelhead redd surveys are feasible, and to train OBMEP staff on observation and recording techniques.