Distribution, Life History and Production of Crayfish in the James River, Virginia

Abstract

-Species composition, distribution, life history and production of crayfish were determined in a 5th-6th-order river in Virginia. Three sites representing distinct geomorphic areas (Ridge and Valley province, Piedmont and Fall Line) were sampled monthly from April 1988 through June 1989. Two species of crayfish, Orconectes virilis and Cambarus bartoni, were collected. Orconectes virilis was only collected from the Ridge and Valley site, whereas C. bartoni was collected from all three sites. Both species had a minimum possible 24-mo lifespan, although few individuals survived past 18 mo. Females extruded eggs in April and by June young were no longer carried by females. Highest growth rates occurred in May and June, during which 68-86% of annual production occurred. The Ridge and Valley site had the greatest abundance of the preferred cobble and boulder substrate. It also had the highest substrate-weighted density (0.4 individuals/M2), biomass (129 mg AFDM/m2) and annual production (155 mg AFDM/m2) of crayfish. Density, biomass and production were much lower at the other two sites, annual substrate-weighted production being only 8-14 mg AFDM/m2. P/B ratios were 0.7-1.1. The predominance of unsuitable habitat, especially a highly embedded substrate, was a primary factor causing the low biomass and production at all three sites.