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



77! 



aged less than 105 organisms/m 2 in June through 

 September (McCabe and Hinton 6 ). However, in a deep 

 area at rkm 120 that had large numbers of YOY white 

 sturgeon, the density of C. salmonis was relatively 

 high in August 1990 (2,289/m 2 ) but dropped to 433 or- 

 ganisms/m 2 in September (McCabe and Hinton 6 ). More 

 research is needed to assess the abundance of benthic 

 organisms in rearing areas of YOY white sturgeon. 



Although prey abundance may be low in many of 

 the deeper areas of the lower Columbia River, the sub- 

 strate in these areas is probably ideal for efficient feed- 

 ing by YOY white sturgeon. The white sturgeon has a 

 protrusible mouth that is used to suck prey from the 

 bottom. In a laboratory experiment with juvenile Rus- 

 sian sturgeon, Acipenser gueldenstaedti, Sbikin and 

 Bibikov (1988) observed that juveniles (<130 mm) pre- 

 ferred even, sandy bottoms to bottoms with stones or 

 depressions. Juveniles avoided vegetated areas. 



Apparently YOY white sturgeon are very effective 

 and efficient predators on prey found in the rearing 

 areas, as evidenced by their rapid growth during the 

 summer and early fall. The YOY white sturgeon 

 reached a mean total length of at least 176 mm by 

 the end of September. Rapid growth during the first 

 growing season reduces natural mortality; by the end 

 of summer or fall, YOY white sturgeon in the lower 

 Columbia River probably have few natural predators. 



Sampling equipment used to collect YOY white 

 sturgeon in the lower Columbia River was limited to 

 two types of bottom trawls that could not be used in 

 shallow littoral areas. Observations made during 

 other studies suggest that YOY white sturgeon do not 

 use shallow littoral areas. No YOY white sturgeon have 

 been collected in intensive beach seining efforts at 

 rkm 75 during the last 15 years. 7 Most sampling was 

 done during daylight; limited sampling was done at 

 night. The beach seining location was adjacent to the 

 sampling site where 52 YOY white sturgeon were col- 

 lected during a 20-hour study in 1990. No YOY white 

 sturgeon were collected in backwaters and shoreline 



6 McCabe, G. T., Jr., and S. A. Hinton. 1991. Report D. In A. A. 

 NigTO led.), Status and habitat requirements of white sturgeon 

 populations in the Columbia River downstream from McNary 

 Dam, p. 145-180. Ann. Rep. to Bonneville Power Admin. (Project 

 86-50) by Oreg. Dep. Fish Wildl., Wash. Dep. Fish., Natl. Mar. 

 Fish. Serv., and U.S. Fish Wildl. Serv. Avail. Bonneville Power 

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



' Richard D. Ledgerwood, National Marine Fisheries Service, P.O. 

 Box 155, Hammond, Oregon 97121. Personal commun., 1992. 



8 McCabe, G. T., Jr., S. A. Hinton. and R. J. McConnell. 1989. 

 Report D. In A. A. Nigro (ed. ). Status and habitat requirements 

 of white sturgeon populations in the Columbia River down- 

 stream from McNary Dam, p. 167-207. Ann. Rep. to Bonneville 

 Power Admin. (Project 86-50) by Oreg. Dep. Fish Wildl., Wash. 

 Dep. Fish., Natl. Mar. Fish. Serv., and U.S. Fish Wildl. Serv. 

 Avail. Bonneville Power Admin., P.O. Box 3621, Portland, OR 

 97208. 



areas during limited beach seining tows in the lower 

 Columbia River in August 1988 (McCabe et al. 8 ). 



We conclude that white sturgeon spawned success- 

 fully in the lower Columbia River during the period 

 1988 through 1991. Collection of YOY white sturgeon 

 indicated that recruitment occurred in all years. 



Acknowledgments 



We thank personnel from the National Marine Fish- 

 eries Service, Hammond, Oregon, and the Washing- 

 ton Department of Fish and Wildlife, Battle Ground, 

 Washington, who assisted in field sampling or sample 

 analyses. Also, we thank Benjamin Sandford for as- 

 sistance with the statistical analysis and two anony- 

 mous reviewers for their constructive comments. The 

 study was funded primarily by the Bonneville Power 

 Administration. 



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