Populations of invasive bighead carp Hypophthalmichthys nobilis in the Mississippi River basin are rapidly increasing in size and range. However, the rate of expansion is not well understood. We used radiotelemetry to document movements of bighead carp within the LaGrange Reach of the Illinois River, Illinois, where populations have been documented since 1993. We surgically implanted radio transmitters into 42 adults in June 2003 and May-July 2004. Successful relocation of individuals decreased over time and ended in August of both years. We analyzed 132 observations from 23 adults and found a mean (6SE) movement rate of 1.70 6 0.74 km/d. The highest movement rate was 14.33 km/d. The maximum distance traveled by an individual was 163 km upstream in 35 d, and the top 10% of movements as observed by boat were between 26.5 and 56.5 km within 3-10 d. Forty-three percent of fish died or dropped transmitters for unknown reasons, but handling, environmental conditions, or both may have contributed to the loss. Our study is the first to document the movement rates and patterns of bighead carp within the United States and shows that adults are capable of moving considerable distances in a short time. Immediate actions to prevent or control their spread are warranted.

Many technical and environmental variables affect radio wave transmission and reception in aquatic environments. We used a controlled experimental design in three large North American rivers (Illinois and Mississippi rivers, Illinois, and Skeena River, British Columbia) to examine the effects of water conductivity, transmitter depth, electromagnetic noise, antenna height, and transmitter type on detection distance. Detection distance was significantly affected by water conductivity, transmitter depth, and electromagnetic noise from a boat motor. Detection distance and maximum depth of signal reception increased with decreasing conductivity except at conductivities from 60 to 90 lS/cm (Skeena River). In contrast to terrestrial radiotelemetry, antenna height did not significantly affect detection distance. We also determined that a transmitter with a 3.5-V battery had an approximately 2.5 times greater detection distance than a transmitter with a 1.5-V battery. We provide quantitative results for several variables influencing radio wave transmission and reception, and we present two regression equations that can be used by researchers to obtain estimated detection distances in rivers of similar conductivity and depth. Furthermore, we compared our detection distances with those calculated from theoretical equations and found that our field results yielded higher detection distances. We strongly believe that there are gaps between results reported in technical papers and those obtained in field method studies; we argue for more collaborative research between aquatic telemetry users and engineers to reduce the current need for trial and error in telemetry study design.