770 



Fishery Bulletin 92|4), 1994 



Dam strongly suggest that eggs are found only in 

 the upper Bonneville Pool, since rkm 298 is about 64 

 km upstream from the dam. 



Spawning in the lower Columbia River in 1988- 

 91 occurred during temperature regimes for success- 

 ful egg incubation. Successful egg incubation for 

 white sturgeon occurs at temperatures between 10 

 and 18°C; highest survival and uniform hatching 

 occur between 14 and 16°C (Wang et al., 1985). In 

 our study, we estimated that peak spawning occurred 

 at water temperatures of 12 to 14°C. We estimated 

 that some spawning occurred at water temperatures 

 of 18 or 19°C. Survival for these eggs was probably 

 less than for eggs spawned at lower water tempera- 

 tures. Wang et al. (1985) observed that substantial 

 white sturgeon embryo mortalities may occur at 

 water temperatures of 18 to 20°C and that tempera- 

 tures greater than 20°C are clearly lethal. In the Sac- 

 ramento River, Kohlhorst (1976) observed that water 

 temperatures during the white and green sturgeon 

 spawning period ranged from 7.8 to 17.8°C and that 

 peak spawning occurred at about 14.4°C. It should be 

 noted that Kohlhorst's estimates of the spawning pe- 

 riod are based on back calculations of larval ages, rather 

 than on sturgeon eggs. Spawning dates can be more 

 accurately estimated by using eggs rather than larvae. 



Sampling for white sturgeon larvae was done with 

 gear that sampled along or very near the bottom; 

 therefore, no data were collected regarding vertical 

 distribution of white sturgeon larvae. However, 

 Stevens and Miller (1970) reported that white or 

 green sturgeon larvae, or both, are primarily demersal 

 in the Sacramento-San Joaquin River System. They 

 caught 33 larvae in 16 bottom sampling efforts and only 

 one larva in eight surface and midwater efforts. 



River currents disperse white sturgeon larvae out 

 of spawning and egg incubation areas. Stevens and 

 Miller (1970) noted a direct relationship between 



river flow and catches of white or green sturgeon lar- 

 vae, or both, in the Sacramento-San Joaquin Delta. 

 In a laboratory experiment, Brannon et al. 5 observed 

 that white sturgeon larvae swam up the water column 

 after hatching. In addition, Brannon et al. 5 found that 

 the behavior of white sturgeon larvae was affected by 

 current velocity in laboratory experiments. There was 

 an inverse relationship between water velocity and the 

 amount of time larvae spent in the water column. 



Dispersal of white sturgeon larvae over a wide area 

 is probably very important in maintaining a stable 

 population of white sturgeon in the lower Columbia 

 River. Wide dispersal allows utilization of more feed- 

 ing areas and rearing habitats by larval and postlar- 

 val white sturgeon and minimizes competition for 

 these limited resources. However, it is also impor- 

 tant that white sturgeon not be carried into saline 

 portions of the Columbia River estuary. Brannon et 

 al. 5 found that salinities >16 ppt killed white stur- 

 geon larvae and fry. 



Food resources for YOY white sturgeon in many of 

 the deeper areas (>12 m) of the lower Columbia River 

 are probably not abundant. Little is known about the 

 diet of YOY white sturgeon in the lower Columbia 

 River; however, limited observations suggest that the 

 amphipod Corophium salmonis is the primary prey 

 (Muir et al., 1988). Densities of C. salmonis in many 

 of the deeper areas probably are low because of un- 

 stable substrates. Corophium salmonis is a tube- 

 builder and requires a more stable substrate to 

 densely populate an area. In 1990, densities of C. 

 salmonis at a deep area ( 19-21 m) at rkm 153 aver- 



5 Brannon, E., S. Brewer, A. Setter, M. Miller, F. Utter, and W. 

 Hershberger. 1985. Columbia River white sturgeon (Acipenser 

 transmontanus) early life history and genetics study. Final Rep. 

 to Bonneville Power Admin. iProject 83-316) by Univ. Wash, 

 and Natl. Mar. Fish. Serv., Seattle, 68 p. Avail. Bonneville Power 

 Admin., P.O. Box 3621, Portland, OR 97208. 



Table 6 



Summary of young-of-the-year white sturgeon, Acipenser transmontanus, catches during a 20-hour study at rkm 75 

 in the lower Columbia River, 31 July-1 August 1990. Sampling was done from 1155 hours on 31 July to 0800 hours 

 on 1 August with a 7.9-m semiballoon shrimp trawl. 



Sunset on 31 July was at 2047 hours; sunrise on 1 August was at 0555 hours. 



