Tuesday, June 5, 2007

Assessment of Population Size, Age Structure and Growth Rates for Cave-Inhabiting Crayfish in Alabama

Michael P. Venarsky, Alexander D. Huryn, Bernard R. Kuhajda, and Jonathan P. Benstead. Department of Biological Sciences, University of Alabama, 201 7th Avenue, A122 Bevill Building, Box 870206, Tuscaloosa, AL 35487

To assess the viability of a species, conservation efforts require population dynamics data from multiple populations across gradients of environmental conditions. Here preliminary results are presented from an ongoing mark/recapture study that is examining the population size, age structure, and growth rate of the obligate cave crayfish Orconectes australis australis and coexisting surface species Cambarus tenebrosus. Carapace length was measured and sex was determined from crayfish collected from four cave streams in the Cumberland Plateau of northeastern Alabama between November 2005 to October 2006. To track individual growth rates and estimate population sizes, a uniquely numbered fluorescent tag was implanted on the ventral side of each individual’s abdomen. Thus far, a total of 226 O. a. australis and 71 C. tenebrosus have been marked. Recapture rates are low (3% to 11%), indicating population sizes are relatively large and/or mobility is high. Only two gravid female O. a. australis have been collected, suggesting reproduction is infrequent. Growth rates appear to be low for both species with only four individuals growing more than two millimeters. Slow growth rates and infrequent reproduction suggest that these crayfish may be incapable of recovering quickly from population declines.