SPAWNING AND EARLY-LIFE HISTORY OF WHITE STURGEON, ACIPENSER-TRANSMONTANUS, IN THE LOWER COLUMBIA RIVER

Spawning and early life history of white sturgeon, Acipenser transmont anus, were studied in the lower Columbia River downstream from Bonnevi lle Dam from 1988 through 1991. From white sturgeon egg collections, w e determined that successful spawning occurred in all four years and t hat the estimated spawning period each year ranged from 38 to 48 days. The spawning period extended from late April or early May through lat e June or early July of each year. Spawning occurred primarily in the fast-flowing section of the river downstream from Bonneville Dam, at w ater temperatures ranging from 10 to 19 degrees C. Freshly fertilized white sturgeon eggs were collected at turbidities ranging from 2.2 to 11.5 nephelometric turbidity units (ntu), near-bottom velocities rangi ng from 0.6 to 2.4 m/s, mean water column velocities ranging from 1.0 to 2.8 m/s, and depths ranging from 3 to 23 m. Bottom substrate in the river section where freshly fertilized eggs were most abundant was pr imarily cobble and boulder. White sturgeon larvae were collected from river kilometer (rkm) 45 to rkm 232, suggesting wide dispersal after h atching. Larvae were collected as far downstream as the upper end of t he Columbia River estuary, which is a freshwater environment. Young-of -the-year (YOY) white sturgeon were first captured in late June, less than two months after spawning was estimated to have begun. Growth was rapid during the first summer; YOY white sturgeon reached a minimum m ean total length of 176 mm and a minimum mean weight of 30 g by the en d of September. Young-of-the-year white sturgeon were more abundant in deeper water (mean minimum depth greater than or equal to 12.5 m) of the lower Columbia River. The results indicate that a large area of th e lower Columbia River is used by white sturgeon at different life his tory stages.