Distribution and Abundance of Chinook Salmon Redds in the Mainstem Trinity River 2002 to 2011

Salmon redds were mapped and carcasses collected in the mainstem Trinity River each fall 2002 through 2011 to quantify and spatially characterize Chinook salmon spawning in the mainstem Trinity River. We applied generalized additive models to the spatiotemporal distribution of hatchery marked or unmarked spawned female salmon carcasses to apportion redd numbers for natural origin and hatchery origin Chinook salmon. These data serve as baseline for the Trinity River Restoration Program to evaluate response of spawning distributions to river rehabilitation and other management actions. Eighteen river rehabilitation sites between Lewiston Dam and the North Fork Trinity River have been implemented over the course of this study. Though spawning distribution responded to physical alterations on a local feature scale (salmon constructed redds in newly created side channels for example), the proportion of redds constructed within the up and downstream boundaries of these rehabilitation sites had not yet significantly changed at broader reach scales. High density spawning area locations remained consistent year to year with little exception. We observed an increase in the mean distance from Lewiston Dam for construction of natural origin Chinook salmon redds over the course of this study. The distribution of hatchery origin Chinook salmon redds remained highly skewed toward Lewiston Dam and Trinity River Hatchery. The number of redds estimated to be constructed by natural origin Chinook salmon females ranged from as low as 2,249 in 2005 to as high as 5,312 in 2011. Estimates of those constructed by hatchery origin Chinook salmon females ranged from as low as 350 in 2009 to as high as 2,269 in 2003. There was no relationship observed in distance downstream of Lewiston Dam that Chinook salmon constructed redds and the yearly total number of Chinook salmon redds.