Characteristics of Harvestable Crayfish Populations in Managed Wetlands of the Lower Mississippi Alluvial Valley

Moist-soil wetlands in the Lower Mississippi Alluvial Valley (LMAV) are managed to provide food resources for wintering waterfowl and also create habitats for native populations of crayfish Procambarus clarkii and Procambarus acutus acutus that may provide a unique fishery to landowners practicing wetland conservation.  To evaluate the feasibility of establishing a fishery for native crayfish in these habitats, we initiated a population assessment of harvestable-size crayfish in moist-soil wetlands in portions of Arkansas, Louisiana, and Mississippi located in the LMAV.  We harvested crayfish using baited pyramid-style traps from 9 wetlands in April-June 2009 and from 15 wetlands in April-June 2010.  We harvested 92.2 kg of crayfish over 1,298 trap nights in 2009.  The average yield was 80 g/trap (CV = 16%).  Procambarus clarkii represented 37% of the total individuals captured while the remaining 62% of individuals were P. acutus acutus.  No females with attached ova were captured.  The carapace length-frequency distribution of crayfish differed significantly across wetlands for each species (Kruskal-Wallis test, p<0.0001).  We harvested 172.2 kg of crayfish over 2,258 trap nights in 2010.  The average yield in 2010 was 87.2 g/trap (CV = 31%).  Procambarus clarkii represented 70% of the total individuals captured.  Only one female with attached ova was captured in 2010.  As in 2009, the carapace length-frequency distribution differed significantly across wetlands for each species (Kruskal-Wallis test, p<0.0001).  To evaluate variation in body condition across wetlands, we conducted an ANCOVA to predict log-transformed weight from log-transformed carapace length for each species.  For P. clarkii, the slope of the length-weight relationship differed across wetlands (F = 63.81, p<0.0001) and between species (F = 33.80, p<0.0001).  Slopes (i.e., b in the traditional W = aL^b equation) ranged from 1.0 to 3.5.  For P. acutus, the slope of the length-weight relationship differed across wetlands (F = 6.95, p<0.0001) but not between sexes (p = 0.9914) and ranged between 2.3 and 3.4.  Crayfish in these habitats are growing allometrically.  One possible explanation in deviations from isometric growth is limited forage quantity.  We are currently processing samples of aquatic invertebrates and standing biomass of vegetation in each of our wetlands to evaluate the relationship between crayfish growth parameters and forage quantity.  We will also present results from our 2011 harvest efforts.  Whereas our yield estimates were less than estimated from high-production rice ponds in Louisiana (e.g., 141 g/trap) our estimates represent expected yields of wild-caught crayfish in moist-soil habitats.