A LONGITUDINAL SURVEY OF DRAGONFLY EXUVIAE IN THE ST. CROIX NATIONAL SCENIC RIVERWAY

Robert Dubois, Wisconsin Department of Natural Resources, Superior, Wisconsin
William Smith, Wisconsin Department of Natural Resources, Endangered Species Bureau
Matthew S. Berg, Grantsburg High School
Joshua J. Watt, Grantsburg High School
Ami S. Cunderla, Grantsburg High School
Ashley J. Goepfert, Grantsburg High School
Amanda M. Huehn, Grantsburg High School
Timothy J. Josephson, Grantsburg High School
Joshua J. Meyer, Grantsburg High School

We quantitatively sampled dragonfly (anisoptera) exuviae from 70 sites on the St. Croix and Namekagon Rivers. An additional 25 sites on six Wisconsin tributaries were also qualitatively sampled. Initial analysis of 16,157 exuviae resulted in 43 species identified. Four species (Ophiogomphus rupinsulensis - 16.6%, Ophiogomphus howei - 12.7%, Gomphurus vastus - 10.6%, and Neurocordulia yamaskanensis - 10.1%) comprised 50% of the sample. Nasiaeschna pentacantha, a species not previously know to occur in Minnesota, was found at two separate sites. Ophiogomphus susbehcha and Ophiogomphus anomalus, Wisconsin endangered and Minnesota threatened species, made up 2.4 and 0.1% of the sample respectively. Susbehcha was found at 29 sites from Riverside Landing to Franconia with a maximum density of 1.48 exuviae/ft of shoreline. Anomolus was more northerly in distribution and rare throughout being found at only ten sites from the headwaters of the St. Croix and Namekagon to Fox Landing, and never reaching a density greater than 0.05 exuviae/ft of shoreline.