Size Selectivity of Gill Nets Used To Target Silver and Bighead Carp in The Upper Mississippi

Bigheaded carp (bighead carp and silver carp) are highly invasive fishes in the Mississippi River System and can be detrimental to native fishes and ecosystems. To limit their impact and further expansion, fishermen have been contracted through state and federal agencies to remove bigheaded carp using predominantly gill nets. Mesh size of entanglement gears determines the size structure of fishes able to be captured. To increase efficiency and effectiveness of bigheaded carp harvest and minimize the capture of bycatch, it is important to understand the relationship of gill net mesh size with the size structure of persistent populations. Therefore, the objective of our study is to determine the size of bigheaded carp and commonly encountered bycatch that are effectively caught in different sized gill nets based on their size. Gill nets were used in pools 16 through 20 on the Mississippi River to capture silver carp and bighead carp. For every 25.4 mm increase in gill net mesh, it was determined that there is a 200 mm increase in the highest retained bigheaded carp body size. With this information, managers will be able to more efficiently target bigheaded carp if knowledge of population size structure is available.