Pilot study of spatial patterns of ichthyoplankton among river Holland-Bartels, L. E., M. R. Dewey, and S. J. Zigler. 1993. Pilot study of spatial patterns of ichthyoplankton among river reaches and habitats of the Upper Mississippi River System. Report by the U.S. Fish and Wildlife Service, National Fisheries Research Center, La Crosse, Wisconsin, for the U.S. Fish and Wildlife Service, Environmental Management Technical Center, Onalaska, Wisconsin, April 1993. EMTC 93-S010. 47 pp. + Appendixes A-C. (NTIS #PB93- 183515) ABSTRACT A pilot study was conducted to evaluate ichthyoplankton communities among selected habitats in the upper Mississippi River. Catch data were used to compare differences in catch among habitat types and to relate these differences to water quality. Sampling design characteristics to describe spatial and temporal differences in the ichthyoplankton community were recommended. Samples were collected by LTRM field station personnel in Pools 8, 13, and 26 of the upper Mississippi River and in the lower section of the Illinois River. About 30% of the samples processed had some sort of collection or recording error. Suggestions were presented to reduce collection and recording errors. Catches in main channel habitats were dominated by freshwater drum Aplodinotus grunniens, whereas cyprinids were dominant in the vegetated backwater habitats. Differences in both species composition and relative abundance occurred between pools. About 50% of the mean density for Pool 8 was freshwater drum, while 82% of the catch from the Illinois River sites was gizzard shad Dorosoma cepedianum. Mean total densities ranged from 166/100 m3 in Pool 13 to 800/100 m3 in the Illinois River. Stations were grouped by composition of the ichthyoplankton community and by water quality parameters. Sample size within each habitat type was insufficient to evaluate among pool variability. Resource allocation analysis indicated that greater effort should be invested in sampling more stations within a habitat type rather than multiple replicates at fewer stations. KEYWORDS Mississippi River, ichthyoplankton, sample design, spatial distribution