762 



Fishery Bulletin 92(4), 1994 



i ' i ' ' i 



f\JO 25 km 



Washington 



rkm 45 



Index site 

 rkm 223 lr k m 230) 



Figure 1 



Location of the white sturgeon, Acipenser transmontanus, study area in the lower 

 Columbia River, 1988-91. 



Trawling was conducted from late March or early 

 April through September or October of each year. In 

 1989, a limited amount of sampling was conducted in 

 early November. Sampling stations were selected to 

 determine the range of habitat used by juvenile white 

 sturgeon and extended from rkm 29 to 218 (Table 1). 

 Trawling effort and geographic range of sampling var- 

 ied among years owing to limited personnel and gear 

 (Table 1). In 1988 and 1989, more trawling effort was 

 concentrated in the river upstream from rkm 120. How- 

 ever, in 1990 and 1991, much more trawling was done 

 in the river between rkm 45 and 120 than in previous 

 years. White sturgeon captured in bottom trawls were 

 measured (total length) and weighed (g). 



On 31 July and 1 August 1990, 14 trawling efforts 

 (7.9-m shrimp trawl) were undertaken from 1155 

 through 0800 hours at rkm 75 to determine whether 

 catches of juvenile white sturgeon, particularly YOY, 

 increased during hours of darkness. 



Physical conditions 



Selected physical parameters were measured in con- 

 junction with biological sampling: minimum and 



maximum bottom depth ( m ); bottom water tempera- 

 ture (°C); bottom water turbidity (ntu); and water 

 velocities at 0.2 of the total depth, 0.8 of the total 

 depth, and about 0.6 m above the bottom. By aver- 

 aging water velocities measured at 0.2 and 0.8 of the 

 total depth, we calculated a mean water column ve- 

 locity (Buchanan and Somers, 1969). Water veloci- 

 ties were measured only during egg and larval sam- 

 pling. Depth was measured with electronic depth 

 sounders, and velocity with a Gurley current meter 

 attached to a 45.4-kg lead fish. A Van-Dorn water bottle 

 was used to collect water samples just above the bot- 

 tom. The water temperature of each sample was mea- 

 sured immediately after collection, and a subsample of 

 water was removed and placed in a glass bottle. The 

 turbidity of the subsample was determined in the labo- 

 ratory with a Hach Model 2 100A Turbidimeter. 



Substrate type was determined from bottom 

 samples collected with a 0.1-m 2 Van Veen grab sam- 

 pler. In addition, a substrate sample was collected 

 at rkm 230 (index site) by scuba divers. Particle size 

 was defined following the classifications presented 

 in Parsley et al. (1993). 



