Green sturgeon habitat suitability varies in response to drought related flow regimes

A series of habitat suitability models were created based upon 2-dimensional tracking of Green Sturgeon and hydraulic simulations. This is an effort to better understand the relationship between the population decline, habitat suitability, and knowledge of the remaining post-dam era habitat available to Green Sturgeon. Records of the movements of Green Sturgeon were collected using a refined acoustic telemetry system (Vemco Ltd., Vemco Positioning System [VPS]) in three pools, the first at rkm 377.0 at the confluence with the Sacramento River of Antelope Creek, the second at rkm 407.5 at the confluence with Inks Creek, and the third at rkm 426.0 at the confluence with Paynes Creek near Red Bluff over a period of two years. The Flow and Sediment Transport with Morphologic Evolution of Channels (FaSTMECH) model was used to simulate depth and velocity. Previously developed habitat suitability curves for spawning Green Sturgeon within the study area were coupled to two-dimensional hydraulic simulations to estimate Weighted Usable Area (WUA), a metric of suitable habitat area within each of the studied reaches. The effect of changing river discharges on suitable spawning habitat for Green Sturgeon was examined over a six-year period, the first of which had normal rain conditions and the following years drought conditions. The peak amounts of spawning habitat in the pool on the Sacramento River at the rkm 377 was the same for all six years, roughly 8000 square meters. The constancy in the amount of WUA, in the face of decreasing rates of discharge may explain why these sites are occupied from year to year. The amount of spawning habitat in the pool at rkm 426, decreased during the four-year drought period, from 2012 to 2015. This may make it less favorable for occupation by Green Sturgeon.