| Summary: | Since the 1980’s, Asian carp (Hypophthalmichthys nobilis and Hypophthalmichthys molitrix) have spread throughout the Mississippi River basin and are now approaching Lake Michigan and the Great Lakes. This poses a problem because Asian carp can have major negative impacts on the zooplankton that support much of the ecosystem. Since Asian carp have invaded the Illinois River, both main channel zooplankton abundance and planktivore body condition have decreased. In an effort to reduce the likelihood of an Asian carp invasion into the Great Lakes, commercial fishing crews are being used to reduce the Asian carp population in the Illinois River. The goal of this project, known as the Barrier Defense Asian carp Removal project, is to reduce the abundance of Asian carp near the barrier at the Brandon Road lock and dam. Zooplankton have recovered from declining planktivory in other aquatic systems: the hope is that the harvesting will reduce the Asian carp’s ecosystem impact on this river as well. The Illinois River response was assessed by comparing the densities of rotifers, nauplii, copepods, and cladocerans in ten backwaters receiving three levels of harvest in late summer of 2015. Analysis indicates that both harvest level and month affect zooplankton, but that there was no interaction. Rotifer densities increased at low (951 kg/km2 month-1) and high (8229 kg/km2 month-1) harvest levels while nauplii, copepods, and cladocerans did not. Cladoceran density decreased from September to October, which may be related to a seasonal succession. In summary, while the zooplankton with the fastest generation time showed a positive response to Asian carp harvest, the current harvesting levels might not be enough for slower growing nauplii, copepods, and cladocerans to respond. The implication of this research is that continuing and even increasing harvest pressure in the future may lead to a stronger general zooplankton response.
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