A 16‐Year Green Sturgeon Population Survey: Investigating River Discharge, Species Identification, Sampling Technology, Survey Extent and Possible Spawning Cyclic Dominance

ABSTRACT Monitoring and understanding the population structure of anadromous fishes is vital to their conservation. The southern distinct population segment of green sturgeon ( Acipenser medirostris ) is a threatened long‐lived anadromous fish, for which we have insufficient information about fundamental aspects of population structure. To gather these data, we began monitoring the population in 2010 with annual surveys using acoustic imagery, and we have recently updated the field and analytical methods. In this work we (1) examine the transition between the two methods using both Dual‐frequency Identification Sonar (DIDSON) and consumer‐grade side‐scan sonar products, (2) use underwater videography to test methodological assumptions about sturgeon species identification, (3) confirm the spatial extent of the spawning grounds with side‐scan sonar and publicly available acoustic telemetry data and (4) update the population estimates. We find the following: there is a consistent detectability relationship between the two acoustic imagery methods, the species we are detecting is indeed green sturgeon rather than a sympatric congener, and the extent of the historical survey covers the entire spawning ground. Through our population estimate update, we find potential evidence for a 4‐year spawning cyclic dominance where one spawning line is significantly larger than the others. The larger line is expected to spawn again in 2026. We believe that this information will be useful to those attempting to recover this species.