AUTHORS: Justin Harms, Graduate Research Assistant, Major - Fisheries Biology - Iowa State University Department of Natural Resource Ecology and Management
ABSTRACT: Invasive Silver Carp (Hypophthalmichthys molitrix) have impacted native fish communities throughout the Mississippi River basin in North America. Previous research has related increases in Silver Carp relative abundance to declines in the condition of native planktivorous fishes and sport fishes that are planktivorous as juveniles due to competition for food resources. However, the effects of a range of relative abundances of Silver Carp on other trophic guilds have not been well-defined. Therefore, our goal was to assess the relationship between Silver Carp relative abundance and body condition of native fishes throughout multiple feeding guilds in the Upper Mississippi River basin. We hypothesize that Silver Carp will alter the trophic ecology and condition of species representing multiple feeding guilds. In addition to resource competition, these influences may represent complex middle-out or spillover effects to the food webs discussed in the literature. We used quantile regression to account for variation in allometric growth described by length-weight relationships to compare body condition of native fish species between sites with different relative abundances of Silver Carp (low and high). We sampled 1,026 individuals from 3 species representing benthic insectivore (Smallmouth Buffalo (Ictiobus bubalus) N=294), piscivore (Flathead Catfish (Pylodictis olivaris) N=256), and omnivore/detritivore (Gizzard Shad (Dorosoma cepedianum) N=476) trophic guilds across 6 rivers and 12 sites where Silver Carp relative abundance spanned a gradient of 0–80 Silver Carp/hour. Our analyses indicated significant differences in body condition were present in Gizzard Shad and Flathead Catfish between sites with high and sites with low relative abundances of Silver Carp. This information can be used by management biologists to understand the effects of Silver Carp on native fish species in recently invaded areas, evaluate management success, and establish targets for population suppression to limit the effects of Silver Carp on freshwater fish communities.
