Effective sampling area: A quantitative method for sampling crayfish populations in freshwater marshes

We used mark-recapture techniques to estimate the attraction sampling area of baited traps for monitoring density of the crayfish Procambarus alleni in the freshwater marshes of the Florida Everglades. We successfully applied a permanent visible tag suitable for mass or individual marking of crayfish. In laboratory mesocosms, males and females and juveniles and adults entered baited wire traps with similar frequency, reflecting a lack of age- or sex-specific bias in trapping. In flooded marsh habitat, we released marked crayfish among a circular array of baited traps set at a specific radial distance from the release point and determined recapture proportions over 48 h. We then used the methodology of Turchin & Odenaal (1996) to estimate the effective sampling area based on the proportions of crayfish recaptured over various radial distances. In flooded marshes, the mean proportion of recaptures declined from 0.59 in traps with a 1-m sampling radius to 0.02 in traps with a 28-m sampling radius. A log-linear regression model provided the best fit to the capture data, and the effective sampling area of baited traps was estimated as 56.3 m(2). The effective sampling area serves as a translation coefficient that can be used to calculate actual density of crayfish in a given area from mark-recapture trapping data.