Deep Water Spawning Observations and Effective Incubation Habitat Modeling for Redband Trout, Spokane River, WA,

Redband trout spawning patches were inventoried and mapped along a 10 mile reach of the Spokane River.  Spawning redds were surveyed during April.  Water depth and velocity measurements at the redds were used to develop spawning habitat suitability criteria.  Spawning and incubation habitat was mapped at each spawning patch over a wide range of discharges.  The empirical data were used to develop continuous spawning and incubation habitat versus discharge relationships at each patch.  The data from the individual patches were combined to create a model of effective spawning habitat for the river over a wide range of initial spawning and end of incubation discharges (1,000 to 25,000cfs ).  Redband trout were primarily spawning in deep water (average depth 3.5 feet, maximum depth 5.3 feet).  The Spokane River typically has a rapidly declining hydrograph in late May/early June prior to emergence.  Deep water spawning protected redds from dewatering.  Effective spawning habitat modeling was used to create a simple flow versus effective spawning habitat matrix tool to help manage flow and spawning habitat.