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Fishery Bulletin 92(4). 1994 



5/16 5/31 6/15 6/30 



Date 



5/16 5/31 6/15 6/30 



Date 



Discharge 



6/15 6/30 7/15 7/30 



./' Temperature 



I 



Spawning Index 



Figure 2 



Water temperatures ( °C ) and Bonneville Dam discharges (mean hourly water discharges by day ) from 1 Apri I through 

 31 July ( 1988-91 ); discharge is shown as m 3 /s x 1,000. Water temperatures were measured at Bonneville Dam. The 

 spawning index shows the days on which we estimated that white sturgeon spawned. 



11.5 ntu, near-bottom water velocities from 1.0 to 2.1 

 m/s, and mean water column velocities from 1.5 to 

 2.6 m/s. Estimated Bonneville Dam discharges at the 

 index site during spawning ranged from 3,890 to 

 9,600 m 3 /s. In all years, the highest egg catches oc- 

 curred during late April or May. 



Results from stepwise regression indicated that 

 water temperature and mean water column velocity 

 together were the best predictors of stage-2 egg col- 

 lections at the index site; however, they explained 

 only 27. 1% of the variation in the egg collections. The 

 regression equation was log 10 (number of eggs plus 

 one/1,000 m 3 ) = 1.01 - 0.110 (water temperature) + 

 0.637 (mean water column velocity); F = 7.99 and 

 P = 0.001. Bottom water turbidity was an important 

 predictor in the first three steps of the stepwise re- 

 gression, but dropped out in the fourth and final step. 

 If a high turbidity value and accompanying zero egg 

 catch (18 April 1989; see Table 3) are removed from 

 the stepwise regression, the results change. Exclud- 

 ing the turbidity data for 18 April 1989, stepwise re- 

 gression indicated that water temperature and turbid- 

 ity together were the best predictors of stage-2 



egg collections at the index site. The regression equa- 

 tion was log U) (number of eggs plus one/1,000 m 3 ) = 

 0.937 - 0.0857 (water temperature) + 1.70 (log 10 tur- 

 bidity); F=11.65, P=0.000, and r 2 =35.7%. Second-de- 

 gree polynomial regression indicated a significant 

 relationship between stage-2 egg collections and 

 water temperature (F=8.70,P=0.001, and r 2 =28.8%). 

 The regression equation was log 10 (number of 

 eggs plus one/1,000 m 3 ) = -4.44 + 0.846 (water tem- 

 perature) - 0.0326 (water temperature 2 ). 



Catches of freshly fertilized white sturgeon eggs 

 during the 12-hour collection at the index site fluc- 

 tuated; catches ranged from 0.0 to 72.2 eggs/1,000 

 m 3 (Table 4). On the basis of collections of freshly 

 fertilized eggs during the 12-hour collection and day- 

 light collections during the 4 years, it appears that adult 

 white sturgeon spawn throughout the 24-hour day. 



Larvae 



White sturgeon larvae were collected from rkm 45 to 

 rkm 232 in the lower Columbia River from 1988 

 through 1991 (Table 2), suggesting wide dispersal 



