AUTHORS: Andrew Glen, Missouri Department of Conservation; Kamryn Wittkop, Missouri Department of Conservation; Tyler Bening, Missouri Department of Conservation
ABSTRACT: The establishment of invasive bigheaded carp (Silver carp Hypophthalmichthys molitrix and Bighead carp Hypophthalmichthys nobilis) in North American river systems over the last few decades has shown to negatively impact native filter-feeding species through direct competition for trophic resources. In the Upper Mississippi River (UMR) system, the Gizzard shad (Dorosoma cepedianum) is one of these impacted species and is frequently encountered in routine monitoring of the Open River Reach of the UMR through the Long Term Resource Monitoring (LTRM) element of the Upper Mississippi River Restoration Program. Because of their high catch rates, monitoring the conditions of Gizzard shad populations in the Open River can be used as an index to how bigheaded carp have and continue to impact native filter feeders over time and as management practices are implemented. Targeted Gizzard shad collections occurred during the observed spring spawning season and in the fall when growth begins to slow for otolith collection. Gizzard shad encountered through LTRM were also included. Individual processing procedures included recording total length, weight, sex, gonad weight, and otolith collection. Otoliths were mounted in resin, cut, and aged. Using this data we calculated Catch per Unit Effort (CPUE), Gonadosomatic Index, body condition, proportional stock density (PSD), and conducted an age and growth analysis. After one season of sampling and analysis, results implied that both CPUE and relative weight were lower than their 5-year average when plotted with existing LTRM data over time. Analysis indicated that while the size distribution appears heavily skewed toward small-bodied fish, PSD remains in the desired range implying there are enough large-bodied individuals and production of age-0 shad is not limiting to the population. Monitoring Gizzard shad condition through time can be used to inform future decisions regarding the success of proposed, established, and newly implemented management techniques for bigheaded carp .
