Chinook Salmon Rearing in a Large Lowland River: Effects of Physical Variables on Nearshore Habitat Use

Factors driving habitat use by juvenile Chinook salmon in large, mainstem riverine habitats remain poorly understood, yet information pertaining thereto is needed to guide restoration and mitigation approaches intended to enhance rearing opportunities for the species. We used point ‐ based boat electrofishing to sample juvenile Chinook during the spring rearing and outmigration season in the Sacramento River over the course of several years, and collected a suite of biologically relevant habitat characteristics at each sampled location, including localized temperature, depth, current velocity, substrate, bank slope and available instream cover. Using logistic regression analysis, we evaluated the effects of physical variables on occupancy probability by juvenile Chinook, and found that a number of habitat characteristics ‐ including temperature, cover, depth, velocity, and others ‐ significantly affect near‐shore habitat use. While some of our findings agree with habitat requirements established on smaller watersheds, others may warrant a reconsideration of restoration and mitigation designs intended to benefit juvenile salmonids in the Sacramento River and other large rivers.