The mark-recapture method applied to population estimates of a freshwater crab on an alluvial plain

Abstract

Mark–recapture methods are a useful population estimation tool, although with many assumptions that cannot always be satisfied for all types of organisms and environments. In the present study, three mark–recapture methods (Petersen, Schnabel and Schumacher–Eschmeyer) were applied in a preliminary trial to estimate the population size of the crab Trichodactylus borellianus and to gain information that would support the use of the methods in the field. The accuracy of these estimates was verified by analysing the percentage of bias, the width of the confidence intervals, and by a chi-square test. The assumptions of equal catchability and closed population were verified, along with assumptions related to the efficiency of marking. The adjusted methodology was applied in a short-term study of a pond on the Parana´floodplain. The results showed that the assumptions were satisfied for both the experimental and field studies. The Schnabel was the most accurate method evaluated in both studies. Although the Schumacher–Eschmeyer method also provided accurate results in the field study, it needed large samples to give reliable estimates. The applicability of these methods depends on the stage of the hydrological cycle. The choice of a short-term research design will ensure that the assumption of a closed population is valid for research of this type on an alluvial plain.