Migration of green sturgeon, Acipenser medirostris, in the Sacramento River

Abstract

Adult green sturgeon, Acipenser medirostris, were collected in San Pablo Bay, California, and surgically implanted with ultrasonic acoustic tags from 2004 to 2006. An array of automated acoustic monitors was maintained in the Sacramento River to record movements of these fish. We presumed movements to known spawning areas (based on previous green sturgeon egg collections) or areas with potential spawning habitat (characterized by substrate, flow, and temperature criteria) represented a “spawning migration.” Three separate annual “spawning migrations” were recorded involving 15 individuals. The majority of the Sacramento River migrants entered the system in the months of March and April. Two different patterns of “spawning migration” and out-migration were observed. Six individuals potentially spawned, over-summered and moved out of the river with the first fall flow event. This is believed to be the common behavior of the green sturgeon. Alternatively, nine individuals promptly moved out of the Sacramento River before 1 September, and any known flow or temperature cue. Some green sturgeon appeared to be impeded on their upstream movement by the 15 May closure of the Red Bluff Diversion Dam, and at least five passed under the dam gates during downstream migration. A delay in the closure of the Red Bluff Diversion Dam would likely allow upstream passage of spawning green sturgeon, further, the potential mortality affects of downstream passage beneath the Red Bluff Diversion Dam should be assessed. Specific protection should be also given to the large aggregation of green sturgeon located in the reach of the Sacramento River adjacent to the Glen Colusa Irrigation District pumping facility.