Abstract
Aquatic invasive species have long been associated with negative ecological and socioeconomic impacts on freshwater ecosystems. In order to mitigate these potential negative effects of invasive species introductions, management and control techniques must be developed. Asian carp species (Silver Carp, Bighead Carp, Grass Carp, and Common Carp) are a problematic group of invasive species that can cause negative effects on native fish species and freshwater ecosystems through a series of trophic cascades. The current focus of Asian carp management and control techniques is directed at reducing population sizes in the upper Illinois River to reduce probability of invasion further upstream at the Illinois River-Great Lakes connection. However, smaller freshwater systems and their associated lakes and impoundments are also vulnerable to invasion and may require management techniques to reduce Asian carp populations. Flooding has resulted in strip mine lakes within the Army National Guard Sparta Training Area being invaded by Asian carps. Therefore, we sought to develop a harvest protocol to remove Asian carps from three Sparta Training Area lakes (S3, S5, and S6) based on a technique developed for Illinois River floodplain lakes that combines multiple net types, electrofishing, and surface sounds and disturbances to drive fish to a pre-determined harvest location. More specifically, lakes were divided into three zones and fish were funneled and herded through strategically-placed monofilament gill nets by surface sounds and disturbances and electrofishing from one end of the lake (zone 1) to the other end of the lake (zone 3) where congregated fish could be more efficiently harvested. To determine our effectiveness of removing Asian carps from these lakes, we used hydroacoustic surveys to estimate reductions in Asian carp density and biomass pre- and post-harvest. A total of 1,232 kg (n = 469) of Asian carps were removed from the three lakes, with much of the biomass being Silver Carp from S5 (n 3 = 250; 720 kg) and S6 (n = 155; 272 kg); S3 contained few Asian carps and removal was minimal (97 kg). Harvest times ranged from 4.25-6.50 hours with a crew of nine people with three boats resulting in 7-14 kg of Asian carp biomass removed per person-hour of work in S5 and S6. Pre- and post-harvest Asian carp density (number of fish / 1000 m3) and biomass (kg / 1000 m3) were reduced by 58-75% in S5 and S6. Effectiveness of the harvest protocol was predicated on our ability to drive fish from zone 1 to zone 3 in each lake. Catch per unit effort for our capture gears was often double to one-hundred fold higher in zone 3 compared to zone 1, indicating that efforts to herd fish into zone 3 were successful. The harvest protocol was effective at removing Asian carps in a relatively short time period. Refining our techniques by adding more zones, or increasing entanglement gears or number of electrofishing boats may improve harvest rates and biomass removed from each lake. The harvest protocol used in this project would likely be applicable to other Sparta Training Area lakes infested with Asian carps that have similar lake morphologies and characteristics; it is unknown how effective this technique will be in larger lakes such as L1, L2 or S11. However, physical barriers would likely be needed at Sparta Training Area lakes to prevent future Asian carp (young-of-year or juvenile) invasions during flooding, particularly lakes in close proximity and elevation to Plum Creek. This study improved our knowledge and techniques for removing Asian carp populations from Sparta Training Area lakes and is anticipated to be applicable to similar small, recreational fishing lakes in other areas. Use of the removal technique described herein would help mitigate the negative ecological effects and nuisances of invasive Asian carps in small lakes. However, future research investigating the techniques used in this study and their effectiveness at removing invasive species should be conducted on lakes with different morphometric characteristics.