Cooperative Fish and Wildlife Research Units Program: all
Education, Research and Technical Assistance for Managing Our Natural Resources

Silver carp, Hypophthalmichthys molitrix, escaped into the Lower Mississippi River (LMR) over 50 years ago, established reproductive populations, and spread across the Mississippi River basin. Demographic rates of silver carp are needed to inform decisions on control and management of this invasive species, but have not been published for the LMR. The purpose of this paper is to report silver carp age and growth estimates from fish collected in riverine (mainstem) and backwater (lake) habitats in the LMR during the period 2011-2019, to compare our results with populations from other geographic areas in the upper Mississippi River drainage, and to evaluate latitudinal and habitat differences in demographic parameters. Silver carp gained weight with increasing length similarly throughout the lower and upper basin. However, annual growth rates were higher in the LMR compared to northern rivers including the Illinois, Wabash, Missouri, and Middle Mississippi Rivers. In the LMR, regression analyses demonstrated that females were heavier in lakes than males or females in the mainstem and that females in lakes had the lowest instantaneous mortality (-0.186). Maximum age was 8 and 10 years for females and males, respectively. The largest male observed was 1022 mm total length (TL), weighed 13.8 kg, and was 7 years old. The largest female was 1036 mm TL, weighed 14.0 kg, and was 7 years old. Rapid growth rates, larger sizes, and lower mortality in the LMR, in combination with limited commercial fishing, extensive river-floodplain connectivity, and vast amounts of spawning areas, ensure that LMR silver carp will continue to act as a source of fast-growing invasive individuals for other reaches and other rivers throughout the Mississippi River Basin.