Food habits of Juvenile American Shad and dynamics of zooplankton in the lower Columbia River

Northwest Science
By: , and 


  • The Publications Warehouse does not have links to digital versions of this publication at this time
  • Download citation as: RIS | Dublin Core


As many as 2.4 million adult American shad annually pass John Day Dam, Columbia River to spawn upriver, yet food web interactions of juvenile shad rearing in John Day Reservoir are unexplored. We collected zooplankton and conducted mid-water trawls in McNary (June-July) and John Day reservoirs (August-November) from 1994 through 1996 during the outmigration of subyearling American shad and Chinook salmon. Juvenile American shad were abundant and represented over 98% of the trawl catch in late summer. The five major taxa collected in zooplankton tows were Bosmina longirostris, Daphnia, cyclopoid cope-pods, rotifers, and calanoid copepods. We evaluated total crustacean zooplankton abundance and Daphnia biomass in relation to water temperature, flow, depth, diel period, and cross-sectional location using multiple regression. Differences in zooplankton abundance were largely due to differences in water temperature and flow. Spatial variation in total zooplankton abundance was observed in McNary Reservoir, but not in John Day Reservoir. Juvenile American shad generally fed on numerically abundant prey, despite being less preferred than larger bodied zooplankton. A decrease in cladoceran abundance and size in August coupled with large percentages of Daphnia in juvenile American shad stomachs indicated heavy planktivory. Smaller juvenile American shad primarily fed on Daphnia in August, but switched to more evasive copepods as the mean size of fish increased and Daphnia abundance declined. Because Daphnia are particularly important prey items for subyearling Chinook salmon in mainstem reservoirs in mid to late summer, alterations in the cladoceran food base is of concern for the management of outmigrating salmonids and other Columbia River fishes. ?? 2006 by the Northwest Scientific Association. All rights reserved.

Study Area

Publication type Article
Publication Subtype Journal Article
Title Food habits of Juvenile American Shad and dynamics of zooplankton in the lower Columbia River
Series title Northwest Science
Volume 80
Issue 1
Year Published 2006
Language English
Contributing office(s) Western Fisheries Research Center
Description 18 p.
First page 47
Last page 64
Country United States
State Oregon, Washington
Other Geospatial John Day reservoir, McNary reservoir
Online Only (Y/N) N
Additional Online Files (Y/N) N
Google Analytic Metrics Metrics page
Additional publication details