|Document Type:||Journal Article|
|Title:||Chinook salmon spawning surveys in deep waters of a large, regulated river|
|Author:||George A. Swan|
|Journal:||Regulated Rivers: Research and Management|
In 1986 research divers surveyed and mapped deep–water spawning redds of fall chinook salmon (Oncorhynchus tshawytscha) in selected sites within an impounded segment of the main–stem Columbia River, Washington State, U.S.A. In velocities over 3 m s–1 and depths up to 11 m, two divers riding a maneuverable sled made cross–current transects communicating observations of substrate materials and deep–water spawning sites. Surface personnel tracked the position of the sled with a laser locating system that logged the information into data storage. Subsequently, the computerized data were translated into overlaying maps depicting location of redds, substrate materials, and depth contours. Deep-water spawning (> 3 m) occurred at most survey sites in velocities between 0.6 and 0.8 m s–1. The average depth of spawning was 6.5 m, and the maximum was 9.1 m—deeper than the depth redds can normally be detected by aerial observation (Sm).
Deep–water spawning ranged from none to substantial in areas of near identical physical characteristics. A method for estimating abundance and density of deep–water redds, based upon the data collected with this mapping technique, is presented. This study combined with current limited information concerning deepwater spawning suggests that up to 80% of the escapement of fall chinook salmon in this reach may spawn in deep water.