Variation in the Density and Population Demographics of Asian Carp throughout the Illinois River

The Illinois River represents the most likely route for Silver and Bighead Carp to invade the Great Lakes.  Asian carp have fully invaded the lower Illinois River, are connected to Mississippi River populations, and can easily move among pools due to wicket dams.  In contrast, Asian carp in the upper river have recently invaded, have limited movement among pools, and are managed through harvest to reduce propagule pressure on the CAWS.  These factors likely result in differences in population demographics throughout the river but a thorough assessment of population demographics is lacking.  This would better inform assessments of ecological impacts and could measure the effectiveness of harvest efforts.  We conducted hydroacoustic surveys throughout the Illinois River (2012-2015) to assess how Asian carp demographics and prevalence vary among pools and years.  Densities were lowest in the upper river, with densities in the uppermost reaches decreasing through time, coincident with harvest efforts.  Asian carp dominated the fish community throughout the river, with the highest relative abundance and biomass estimates approaching 46% and 78% of the fish community, respectively.  Relative abundance and biomass were lower in the upper river but did not differ between main channel or backwater habitats in any pool.