The Okanogan River contains the furthest upstream and northern-most extent of currently accessible anadromous salmonid habitat in the Upper Columbia River. Adult steelhead migrate upstream from the ocean in the summer months, over-winter in the upper Columbia or Okanogan River, and spawn the next spring from March through late-May. During spawning, female steelhead use their tails to create a nest where eggs are deposited. This nest is also referred to as a redd. The moving water washes the substrate downstream, allowing the female to lay her eggs in the remaining depression. Once the male(s) fertilize the eggs, the female covers the eggs by fanning the substrate upstream of the redd. This leaves a distinguishable pit with a mound on the downstream end (the tailspill). During this process, periphyton and fine sediment are removed from the disturbed substrate, making the redd readily distinguishable from the surrounding substrate.
Steelhead spawning surveys, also called redd surveys, are conducted throughout the Okanogan subbasin on the mainstem Okanogan and Similkameen Rivers and all tributaries that contain sufficient water to support spawning. The process begins with two surveyors on pontoon boats floating down the mainstem river searching for redds. In small tributaries, two individuals walk in or along the stream while searching for redds, beginning at the mouth of the creek and proceeding upstream. When redds are discovered, the depth of the redd is measured, the location is recorded with a GPS point, and the redd is flagged along the bank to prevent double-counting in future surveys.
In addition to redd surveys, OBMEP has also operated several underwater video monitoring stations to count numbers of adult salmonids passing fixed points. The station at Zosel Dam, located on the downstream end of Osoyoos Lake, operates continuously while video stations on Salmon Creek, Ninemile Creek, and Antoine Creek have been only operated during the steelhead spawning season. Video data are recorded with a digital video recorder (DVR) which is linked to the internet. Staff members review the video data remotely from the office. Target species include steelhead, Sockeye, Chinook, and occasional observations of Coho salmon; however, all resident fish species are also recorded.
PIT Tag Detections
Adult steelhead are also monitored through Passive Integrated Transponder (PIT) tag detections at interrogation sites located throughout the Okanogan subbasin. PIT tag detections at fixed antenna sites are used to define timing of movements, spatial distribution of spawning, passage success through an impediment (e.g. culvert or small waterfall), and estimate total spawner abundance, among others. For more information on monitoring steelhead with PIT tags, refer to the PIT Tag Interrogation page.