FEEDING ECOLOGY OF JUVENILE WHITE STURGEON NACIPENSER-TRANSMONTANUS) IN THE LOWER COLUMBIA RIVER

The white sturgeon (Acipenser transmontanus) supports important recrea tional and commercial fisheries in the lower Columbia River. Little is known about the ecology of white sturgeon, and the feeding ecology in particular has received only limited investigation. From April throug h October 1988, the feeding ecology of juvenile white sturgeon was stu died in two areas of the lower Columbia River. Overall, the tube-dwell ing amphipod Corophium salmonis was the most important prey for the tw o size classes of juvenile white sturgeon studied. However, during all sampling periods and at both areas (River Kilometers [RKm] 153 and 21 1), Size Class I white sturgeon (144-350 mm fork length) preyed more heavily on C. salmonis than did Size Class II white sturgeon (351 to 7 24 mm). Other temporally important prey for Size Class I white sturgeo n included Corophium spinicorne, Neomysis sp., Chironomidae larvae, an d eulachon (Thaleichthys pacificus) eggs; other temporally important p rey for Size Class Il white sturgeon included the bivalve Corbicula fl uminea, Corophium spinicorne, Chironomidae larvae, and eulachon eggs. Index of Feeding analysis indicated that juvenile white sturgeon in bo th areas contained less food in September-October than in either May-J une or July-August. Generally, the relationships between densities (ab undances) of specific benthic organisms and white sturgeon diets were poor at RKm 153 and 21 1. Despite the importance of Corophium salmonis in the diets of juvenile white sturgeon, it was not abundant in the b enthos (mean density, < 185 organisms/m2 in April and September).