Can Productivity Measurements Predict Asian Carp Hotpots?

Information on habitat use by Asian carps is sparse and most research has occurred on large rivers (e.g., Yangtze, Missouri, Illinois), however, we observed dense concentrations in smaller tributary mouths in South Dakota.  Research on larger rivers indicated that silver carp select habitats with lower water velocities and higher phytoplankton abundances. Thus, we predicted that tributary mouths are preferred habitats for Asian carps. We sampled six paired sites (i.e., mainstem and tributary) across seasons from 2012-2013 to compare nutrient enrichment, water clarity, potential stressors and food resources. Additionally, fish were sampled at three paired sites.  Differences were compared between habitats using paired t-tests.  Contrary to our hypotheses, nutrients were not different between habitats; however, water clarity variables were higher in the mainstem as compared to tributaries.  Similarly, Asian carps were more abundant in mainstem habitats although catches were variable between drought and flood years.  Additionally, habitats did not differ in the number of plankton taxa and both were dominated by diatoms.  Lack of productivity differences between habitats could be reflective of drought conditions.  Finally, Asian carps may not be selecting tributaries as our field observations suggested, but may be selecting for higher velocities typical of mainstem habitats.