Ethan Mora and Steve Lindley of the SWFSC Fisheries Ecology Division completed a survey aimed at estimating the abundance of green sturgeon in the Rogue River, Oregon. The project is a collaboration with Dan Erickson of the Pew Institute for Ocean Science and the Oregon Department of Fish and Wildlife.
Previous work in the Rogue River using acoustic and radio telemetry has shown that green sturgeon reside in areas of the river with depth > 15 m, and all such areas were mapped and surveyed with a dual-frequency identification (DIDSON) sonar. Estimates of sturgeon abundance can be made from multiple DIDSON passes using the method of bounded counts under certain conditions. Traditional capture-mark-recapture methods were employed to verify that these conditions were met, to get independent estimates of abundance in a subset of holding areas, and to collect biological specimens, including fin clips for population genetics and blood serum for sex identification.
The DIDSON appears to be an extremely effective tool for observing green sturgeon, which were found to be highly aggregated in a small subset of suitable habitat areas. Lindley, Mora, and Erickson look forward to producing the first estimate of the size of a green sturgeon population, which will give some perspective on observed landings of this species of concern. They also hope to apply these techniques to the Sacramento River green sturgeon, a threatened species under the ESA. This project was supported by the NMFS Species of Concern Program. (October 25, 2007)