Some factors regulating cohort production of the crayfish, Orconectes virilis

SUMMARY. Cohort production of the crayfish. Orconectes virilis , ranged from 148.8 to 70.2 kg in North Twin Lake (surface area 1.9 ha) and from 151.9 to 84.9 kg in West Lost Lake (surface area 1.4 ha). Both cohort production (P) and cohort mean biomass (B) showed a long-term decrease with time. The cohort P/B ratios did not show such a trend but remained steady. The P/B ratio approximated the life cycle instantaneous rate of growth (G) which could then be used for estimating cohort production from mean biomass.
Production remained consistently higher in West Lost Lake. Analysis of horizontal life table data revealed no inherent difference between survival and fecundity rates of the crayfish population in each lake. Slight differences in basin morphometry between the two lakes determined nursery habitat availability and this affected recruitment of young from each female brood stock. Small differences in carrying capacity between two similar sized nearby lakes, along with a decrease in carrying capacity over time, were sufficient to nullify attempts to manage these populations using a maximum sustainable yield model.