Potential Effects of Invasive Species on Paddlefish
Mark A. Pegg, John H. Chick, and Brenda M. Pracheil
Abstract.—Invasive species are one of the dominant problems fisheries managers face when dealing with management, conservation, or preservation of native fishes. The primary concern is the potential for negative interactions between invasive and native species where the outcome is reduced abundance, fitness, growth, or extirpated native fish species. These negative interactions can come from direct competition for resources, vectors for the spread of disease or parasites, and subtle effects such as altering the flow of energy within and among other trophic levels. Paddlefish Polyodon spathula are not exempt from these threats and may even be at a higher risk because they are endemic to historically lotic systems in the central United States where many invasive species are now becoming established. The most prominent invasive threat to paddlefish may be from fellow filter-feeders bighead carp Hypophthalmichthys nobilis and silver carp H. molitrix because they consume similar food resources, possibly displace other pelagic species, and can also change the plankton community to one that cannot be as efficiently used by paddlefish. These two carp species have had a negative influence on native fish communities in other parts of the world, and have been shown to negatively interact with juvenile paddlefish in North America. Response plans that implement a movement barrier or removal of invasive species may also have ramifications for paddlefish in that they restrict movement patterns or reduce abundances as bycatch through harvest schemes. Gaining insights into potential invasive species threats to paddlefish is critical so that informed decisions can be made to prevent ecological damage from the invasive species while optimizing sustainability of native species.