Spawning Habitat Used by Fall Chinook Salmon in the Snake River

Abstract

Literature describing spawning habitat used by fall-run chinook salmon Oncorhynchus tshawytscha is lacking for populations using large, main-stem rivers. A stable spawning flow regime in the Snake River below Hells Canyon Dam and enhanced survey capabilities using remote underwater videography allowed us to accurately describe spawning habitat used by fall chinook salmon within this large river. Water depth measured at 205 fall chinook salmon redds ranged from 0.2 to 6.5 m. Mean water column velocity at 145 redds ranged from 0.4 to 2.1 m/s, and substrate- level water velocity at 164 redds ranged from 0.1 to 2.0 m/s. Substrate size classifications from 112 redds indicated that areas having particle sizes that are relatively homogenous with diameters of 2.5–15.0 cm are used for spawning. During our study, spawning generally began as water temperatures dropped below 16.0°C, and concluded as temperatures approached 5.0°C. Our results corroborate earlier observations of fall chinook salmon spawning in deep, fast-velocity water in the Hanford Reach of the Columbia River and significantly expand current criteria used to model spawning habitat availability for these fish within large rivers.