Assessment of Sampling Gears for Bigheaded Carp in Mid-order Prairie Rivers in Nebraska

Silver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis (collectively bigheaded carp) have invaded tributaries to the Missouri River and Platte River in Nebraska, USA. Information pertaining to efficient sampling protocols for assessing bigheaded carp populations as well as benefiting removal efforts is needed. Herding is a method used to increase the capture efficiency and detection probability of adult bigheaded carp by simultaneously using active and passive sampling gears. During June-July 2023, four herding techniques were assessed regarding their ability to elicit directional movement past an enclosure gate. The combination of sound and electrofishing resulted in the highest mean number of bigheaded carp successfully herded, followed by electrofishing, sound, boat and motor only, and the control. Mean depth was shown to influence herding effectiveness and exhibited a positive relationship. During the summer of 2024, boat electrofishing and herding with gill nets were conducted on three tributaries of the Missouri River and one tributary of the Platte River and compared based on capture efficiency and cost-effectiveness. A total of 6,205 bigheaded carp were collected, with herding resulting in the capture of 2.8 times more bigheaded carp than electrofishing. Herding (437.3 fish/hr) had a higher mean catch-per-unit-effort (CPUE) than electrofishing (155.0 fish/hr) when accounting for gear effort (i.e., run time). However, electrofishing (39.0 fish/person-hr) had a greater CPUE than herding (20.1 fish/person-hr) with the inclusion of overall effort (i.e., labor hours and crew size). In achieving an equivalent weekly catch, electrofishing was more cost effective than herding. The results of this study will provide managers, researchers, and stakeholders knowledge regarding efficient and cost-effective sampling strategies for invasive bigheaded carp that enable assessments of presence and population status as well as provide control options for population reduction and potential removal. Advisor: Jonathan J. Spurgeon