Invasive silver carp (Hypophthalmichthys molitrix) populations have expanded greatly in the Upper Mississippi River System (UMRS) since their introduction in the early 1970s. We conducted a Chapman-modified, continuous Schnabel mark-recapture population and biomass estimate for silver carp (106-901 mm) in the La Grange reach, Illinois River during 2007-2008. We estimated a total of 328,192 (95% CI 231,226-484,474) silver carp (2,544 per river km 1,792-3,756) comprising 705 (95% CI; 496-1,040) metric tons of biomass (5.5 metric tons per river km 3.8-8.1). Long Term Resource Monitoring Program (LTRMP) data from the La Grange reach showed an exponential increase in silver carp catches since 1998, with an intrinsic rate of increase approaching 84%. In 2008, silver carp comprised about 51% of the total LTRMP annual fish collection. To our knowledge, this large river reach may contain the greatest ambient densities of wild silver carp in the world. Our findings provide a target for reduction efforts and also emphasize the importance of the La Grange reach as a source population for potential expansion of the species to the Laurentian Great Lakes. (c) 2009 Springer Science+Business Media B.V.
Sass, G. G., Cook, T. R., Irons, K. S., McClelland, M. A., Michaels, N. N., O'Hara, T. M., & Stroub, M. R. (2009). A mark-recapture population estimate for invasive silver carp (Hypophthalmichthys molitrix) in the La Grange Reach, Illinois River. Biological Invasions, 12(3), 433--436. https://doi.org/10.1007/s10530-009-9462-z