Movements and Habitat Use by Grass Carp in a Large Mainstream Reservoir

Abstract

Triploid grass carp Ctenopharyngodon idella were experimentally stocked in a large, open, mainstream reservoir on the Tennessee River so we could describe their movement and dispersion patterns and determine if areas infested with hydrilla Hydrilla verticillata were preferentially used. Radio transmitters were surgically implanted in 25 immature grass carp in 1987 and 10 mature fish in 1988. Dispersion and use of vegetated habitat were analyzed separately for summer (warmwater) and fall-spring (coldwater) periods for grass carp stocked in 1987. The fish moved an average of 2.2 km (0.5–6.3 km) during summer 1987 and 0.4 km during the fall-spring period. The grass carp marked in 1987 tended to move upstream during the summer, ranged over an average area of only 0.10 km2 (0.02–0.30 km2), and moved even less during the fall-spring period. The submersed plant communities most used by the grass carp in 1987 were dominated by hydrilla and all relocated fish were in vegetated areas. The adult grass carp marked in 1988 moved an average of 32.7 km (0.7–71.1 km) during a 4-month monitoring period, did not reduce movements when water temperature declined, traveled both upstream and downstream, and ranged well beyond hydrilla colonies. The difference in behavior between fish stocked in 1987 and those stocked in 1988 appeared to be related to life history stage (juveniles versus adults). Thus, juvenile triploid grass carp seem more likely to provide effective hydrilla control in target areas than adults.