Silver carp (Hypophthalmichthys molitrix) are one of five species of Asian carp that have successfully invaded the Upper Mississippi River System and established reproducing populations. This species spawns in rivers when water temperature is ≥ 18⁰C and there is a rise in the water level. Trends of increased water temperature and increased frequency and magnitude of flooding in the Upper Mississippi River System appear to be beneficial to the reproductive success and recruitment of silver carp. During the summer of 2015, we examined the use of “edge of flood” habitats by larval silver carp during the extensive flooding that occurred in Pool 26 and the Middle Mississippi River, and the confluence of the Illinois River with the Upper Mississippi River.
We captured over 12,700 individual fishes from eight taxa using small aquarium nets in shallow water (i.e., < 0.5 m) at the edge of the flood. Over 12,000 of these individuals (> 95%) were silver carp larvae between 5 and 21 mm standard length. Peak catch rates occurred near the confluence of the Illinois and Mississippi rivers. This study suggests the affinity for larval silver carp to move with the edge of a flood has been under-appreciated. The high catch rates observed at the confluence of the Illinois and Mississippi rivers raises the question of whether this is a unique instance or whether other major river confluences will also be hot zones for larval silver carp.