McCabe and Tracy: Spawning and early life history of Acipenser transmontanus 



761 



Although white sturgeon supports important fish- 

 eries in the Columbia River and other rivers within 

 its range, little is known about the spawning char- 

 acteristics and early life history of this long-lived 

 species. Using larval collections, Stevens and Miller 

 (1970) described the distribution of white or green, 

 A. medirostris, sturgeon larvae, or both, in Cali- 

 fornia's Sacramento-San Joaquin River system, and 

 Kohlhorst ( 1976 ) described sturgeon spawning in the 

 Sacramento River. Parsley et al. (1993) described 

 spawning and rearing habitats of white sturgeon in 

 the Columbia River downstream from McNary Dam; 

 however, important specific information about 

 spawning and early life history of white sturgeon in 

 the Columbia River downstream from Bonneville 

 Dam was not presented. 



From 1988 through 1991, we studied spawning 

 characteristics and early life history of white stur- 

 geon in the lower Columbia River. Primary goals of 

 the study were 1) to define where and when spawn- 

 ing occurred and 2) to assess the environmental con- 

 ditions at the time of spawning. Additional goals were 

 to determine larval distribution and habitat use by 

 young-of-the-year (YOY) white sturgeon. 



Methods 



Egg and larval sampling 



From 1988 through 1991, white sturgeon eggs and lar- 

 vae were collected in the Columbia River downstream 

 from Bonneville Dam. The collection period varied 

 among years; however, in all years, it extended from 

 at least April through early July. Generally, samples 

 were taken weekly during this period. A D-shaped 

 plankton net was used to collect white sturgeon eggs 

 and larvae. This net was 0.8 m wide at the bottom of 

 the mouth opening, 0.5 m high, and constructed of 

 7.9-mesh/cm nylon marquisette netting. Depending 

 on water velocity, two to six lead weights (4.5 or 9.1 

 kg each) were attached to the net frame to hold the 

 net on the river bottom. A digital flow meter (Gen- 

 eral Oceanics Model 2030) was suspended in the 

 mouth of the net to estimate the volume of water 

 sampled. Typically, two plankton nets were fished 

 simultaneously for about 30 minutes from an an- 

 chored 12.2-m research vessel. When water veloci- 

 ties at 0.2 of the total depth were greater than 2 m/s 

 and other adverse sampling conditions were present, 

 only one plankton net was fished, often for one hour. 

 Artificial substrates constructed of latex-coated 

 animal hair also were used to collect white sturgeon 

 eggs (McCabe and Beckman, 1990). Each artificial 

 substrate, which was 76 x 91 cm, was enclosed in an 

 angle-iron frame. The substrate and frame were held 



in place on the bottom with a three-fluke anchor simi- 

 lar to a grapnel. A buoy line was attached to the an- 

 chor to allow retrieval of the substrate, frame, and 

 anchor. Artificial substrates were generally retrieved 

 and examined weekly for eggs. 



In 1990 and 1991, a 3.0-m beam trawl was used 

 weekly or biweekly in late June, July, and August to 

 collect white sturgeon larvae and YOY. The estimated 

 fishing width of the trawl was 2.7 m and the height 

 was 0.5 m. A 1.59-mm knotless nylon liner was in- 

 serted into the body of the net. The beam trawl was 

 towed slowly upstream along the bottom for periods 

 ranging from 2 to 20 minutes. 



White sturgeon eggs and larvae were initially pre- 

 served in an approximately 4% buffered formalde- 

 hyde solution. After the eggs and larvae were pro- 

 cessed in the laboratory, they were transferred to a 

 20% methanol solution. Processing of the eggs and 

 larvae was done within 60 days after collection. 



White sturgeon egg or larval sampling was con- 

 ducted at various sites in the lower Columbia River 

 from rkm 29 to 234 (Table 1, Fig. 1). Following ex- 

 ploratory research conducted in 1987, we decided to 

 concentrate egg and larval sampling with station- 

 ary gear (plankton nets and artificial substrates) 

 between rkm 172 and 234. We selected a site at rkm 

 230, used in previous research for monitoring white 

 sturgeon spawning, for the most frequent egg sam- 

 pling. We call this the index site. 



In 1988, a 12-hour collection with a plankton net 

 was made at the index site to determine whether 

 catches of white sturgeon eggs and larvae changed 

 during different light conditions. The study began 

 at 1843 hours on 25 May and ended at 0623 hours on 

 26 May. Normally, one plankton net was fished for 

 one hour during each sampling effort; 11 sampling 

 efforts were made. 



Young-of-the-year sampling 



A 7.9-m (headrope length) semiballoon shrimp trawl 

 was used to collect juvenile white sturgeon, includ- 

 ing YOY, from 1988 through 1991. Mesh size in the 

 trawl was 38 mm (stretched) in the body; a 10-mm 

 mesh liner was inserted in the cod end. Trawling ef- 

 forts with the shrimp trawl were normally five min- 

 utes in duration in an upstream direction, beginning 

 when the trawl and the proper amount of cable were 

 deployed, and ending five minutes later. Trawl speed 

 over the bottom was usually 3 to 5 km/hour. In 1990 

 and 1991, a 3.0-m beam trawl was also used to collect 

 YOY white sturgeon (see Egg and Larval Sampling 

 section). Using a radar range-finder, we estimated the 

 distance fished during each sampling effort. Beam trawl 

 speed over the bottom was usually 1 to 3 km/hour. 



