COMMON CARP (\u3ci\u3eCYPRINUS CARPIO\u3c/i\u3e) POPULATION CHARACTERISTICS AND RECRUITMENT IN TWO NEBRASKA SANDHILL LAKES

Common carp (Cyprinus carpio) are a non-native fish in the United States. Due to their prolific nature, they may have detrimental effects on fish and waterfowl communities, including those of Nebraska Sandhill lakes. Information regarding population structure, age, and growth of common carp in Nebraska Sandhill lakes is lacking. We examined adult common carp populations from Marsh and Pelican lakes on the Valentine National Wildlife Refuge. We described size and age structure, growth, and recruitment patterns for these two populations. Age-frequency histograms revealed consistent recruitment of common carp through age 7 in Marsh Lake but inconsistent recruitment in Pelican Lake. Common carp growth was initially faster in Pelican Lake than in Marsh Lake, likely because of a less dense carp population in Pelican Lake. Pelican Lake contains northern pike (Esox lucius) and largemouth bass (Micropterus salmoides), top-level piscivores, while Marsh Lake contains no predatory fish species. The absence of top-level piscivores preying on age-O common carp may have led to the denser population in Marsh Lake. Further research is recommended to understand fully the role of common carp in Sandhill lake communities. Common carp (Cyprinus carpio) have been introduced into many water bodies throughout the world, including Europe, Australia, and North America (Vooren 1972, Shearer and Mulley 1978, Mills et al. 1993). The wide distribution and successful introductions of common carp are largely due to their tolerance of varying environmental conditions (Forester and Lawrence 1978). Their ability to thrive in new water bodies has caused many ecosystem management problems. Common carp can affect the abiotic aspects of aquatic communities substantially. For example, common carp have been shown to increase turbidity, total phosphorus, and ammonia concentrations (Lougheed et al. 1998, Angeler et al. 2002). Also, high population abundances have been positively correlated with increases in chlorophyll a levels, increased nitrogen concentrations, and an increased amount of suspended solids (Angeler et al. 2002, Parkos et al. 2003). Common carp can also have detrimental effects on the biotic potential of aquatic ecosystems directly and indirectly through their feeding and spawning habits (Zambrano and Hinojosa 1999). Common carp can reduce abundances of submerged macrophytes and macroinvertebrates (Crivelli 1983, Parkos et al. 2003). As a result, common carp can thus affect the abundance of recreational fish species and waterfowl that depend on macrophytes and macroinvertebrates for food and cover at various life stages (Forester and Lawrence 1978). Because common carp can have substantial impacts on aquatic ecosystems, understanding basic population characteristics is a necessary first step to determine appropriate management strategies. This information, however, is lacking for populations in Nebraska Sandhill lakes. Therefore, our objective was to describe the size and age structure, growth, and recruitment patterns of common carp in Marsh and Pelican lakes, Nebraska