Management Implications from a Stock-Recruit Model for Bighead Carp in Portions of the Illinois and Mississippi Rivers
Michael H. Hoff, Mark A. Pegg, and Kevin S. Irons
Abstract.—The Aquatic Nuisance Species Task Force, Mississippi River Basin Panel on Aquatic Nuisance Species, Mississippi Interstate Cooperative Resource Association, and other entities established goals to control feral populations of bighead carp Hypophthalmichthys nobilis in the United States. The Asian Carp Working Group recommended development of stock-recruit models for bighead carp and other Asian carps to assist in management and control of feral populations. We developed a Ricker stock-recruit model, using bighead carp relative abundance data collected in the LaGrange Reach of the Illinois River and Pool 26 of the Mississippi River during 2001–2004, to guide management and control efforts there. The functional relationship that explained the greatest amount of recruitment variation explained 83% of the recruitment (during July through October of the first year of life) variation using stock size and river discharge. Seventy-two percent of recruitment variation was explained by stock size abundance while an additional 11% was explained by the coefficient of variation of discharge in July. Model predictions and empirical data indicated that management efforts to reduce stock size abundance from the optimum of 0.07 adults per unit of standardized fishing effort to 0.02 adults per unit of effort should be the most effective tool to reduce recruitment over the long term. This level of adult abundance (approximately 25% of the mean during 2001–2004) should be the target maximum for bighead carp control efforts in the study areas. Recruitment was inversely correlated with variation in river discharge, so it is possible to combine control of stock size abundance and management of river discharge in an integrated pest management program for bighead carp in the two river reaches.