Distributions and selected aspects of the life histories and habitat associations of the crayfishes Orconectes peruncus (Creaser, 1931) and O. quadruncus (Creaser, 1933) in Missouri

The crayfishes Orconectes peruncus and O. quadruncus are endemic to the upp er St. Francis River drainage in southeastern Missouri, and were classified as threatened in a recent analysis of the conservation status of crayfishe s in the United States and Canada. Their distributions are not documented a nd little is known about their ecologies. In addition, recent collections s uggested that the introduced crayfish O. hylas may be displacing O. quadrun cus from its type locality, Stouts Creek (Madison and Iron counties). The p urpose of our study was to assess and compare the distributions and selecte d aspects of the life histories and habitat associations of these crayfishe s. Sampling at 57 sites on 30 streams in the upper St. Francis River draina ge fi from October 1996 through March 1998 showed that O. peruncus was more widespread and more abundant than O. quadruncus. The two species were symp atric in only three streams. Patterns of reproductive events in the species ' annual life cycles were similar, although O. peruncus showed signs of mat ing activity a month earlier than O. quadruncus. The crayfishes showed simi lar habitat associations. Orconectes quadruncus has been largely displaced from Stouts Creek by the introduced O. hylas. Orconectes hylas also potenti ally threatens O. peruncus in Big Creek, warranting further study.