Life histories of two populations of the imperiled crayfish Orconectes (Procericambarus) Williamsi (Decapoda: Cambaridae) in Southwestern Missouri, U.S.A.

The imperiled Williams' Crayfish, Orconectes williamsi Fitzpatrick, 1966 is endemic to southwestern Missouri and northwestern Arkansas, U.S.A., an area experiencing rapid urbanization and other land use changes. Populations of O. williamsi in two small streams were studied for 26 months to describe annual reproductive cycles, and gather information about fecundity, sex ratio, size at maturity, size-class structure, and growth. We captured a monthly average of more than 120 O. williamsi from each of the two study populations. The life history of O. williamsi appeared generally similar to what has been reported for several other stream-dwelling species of Orconectes. Breeding season occurred in mid to late autumn and perhaps into early winter. Egg brooding occurred during late winter and early spring, although it was difficult to locate females carrying eggs or hatchlings. Young of year first appeared in samples during May and June. We estimated that these populations of O. williamsi contained 3 or 4 size-classes; smaller O. williamsi grew faster than larger individuals and the mean specific growth rate was about 2% per day during summer. Life history information presented herein will be important if expected future conservation efforts are required.