Habitat Preference, Dispersal, and Population Trends of Three Species of Invasive Asian Carps in Tributaries of the La Grange Reach of the Illinois River
ILLINOIS NATURAL HISTORY SURVEY URBANA
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Asian carps Ctenopharyngodon idella, Hypophthalmichthys molitrix, and H. nobilis, first introduced into the United States in the 1960s and 1970s, escaped and established reproducing populations in the Mississippi and Illinois River systems by the year 2000. By the mid 1990s, they were appearing in smaller tributaries and streams in Illinois. During the summer of 2009, a drainage-wide survey of the La Grange Reach of the Illinois River was conducted to determine the extent to which these species were utilizing first- through fourth-order streams in this system. Field sampling of 36 sites over a 33,636-km2 area in 2009 produced a total of five grass carp and no other Asian carp specimens, indicating temporary nonresident utilization of small streams. Because of the paucity of Asian carp specimens collected during field work, field data were combined with records from the Illinois Natural History Survey Fish Collection, Illinois Department of Natural Resources survey data, and the Long Term Resource Monitoring Program. These data were subjected to statistical analysis to test for correlation of population trends between the Illinois River mainstem and its associated tributaries. Analysis results revealed a positive relationship between annual mainstem and tributary population trends for grass carp and silver carp, as well as a continually increasing population size for all three species in both mainstem and tributary populations.