Competitive Interactions Between Bighead Carp and Bluegill

Invasive species are a driving force of global ecosystem change.  Asian carp (bighead carp Hypophthalmichthys nobilis and silver carp H. molitrix) are invasive obligate planktivores that established in the Mississippi River Basin in the 1970s, and since then their populations have grown exponentially.  The full implications of their influences on native fishes in the Mississippi River Basin are unclear. While previous research demonstrated that Asian carp are associated with degraded body condition of native planktivores such as paddlefish (Polyodon spathula), bigmouth buffalo (Ictiobus cyprinellus), and gizzard shad (Dorosoma cepedianum), research is lacking for facultative planktivores.  Using bluegill (Lepomis macrochirus) as my facultative planktivore species, I manipulated densities of both bluegill and bighead carp in a mesocosm experiment to better understand how these two species may influence each other by competing for limiting zooplankton.  We found that bluegill stocked in low densities exhibited a linear decrease in size with increasing bighead carp densities.  Bighead carp did not display similar density dependence; instead, intraspecific competition appeared to be most influential when the carp were stocked at high densities regardless of total fish density.  This research can contribute to our growing understanding of the influences Asian carp exert on our native fish populations.