Estimating the Population Size of Aegla Franca (Decapoda: Anomura: Aeglidae) by Mark-Recapture Technique from an Isolated Section of Barro Preto Stream, County of Claraval, State of Minas Gerais, Southeastern Brazil
Abstract The Schumacher-Eschmeyer and the Schnabel estimators for closed population were employed to estimate the population size of Aegla franca from an isolated section (30 m long; area: 76.125 m2) of the Barro Preto stream (20°18′47″S; 47°16′37″W) in the summer and winter seasons of the year 2005. These methods involve mark-recapture technique with multiple sampling, and each season estimate was conducted for eight consecutive days. The study area was isolated with a 4 mm mesh net to prevent migration of aeglids into or out of the study area. Traps were randomly set overnight and inspected for captured aeglids in the following morning. Two marking techniques were employed separately: a mixture of silver purpurin powder and fast-drying glue gel (summer estimate) and cauterization by red-hot pin head (winter estimate). All unmarked individuals from each sampling event were sexed, had their carapace length measured and were then marked, and released back in midpoint of the isolated area of the stream along with previously marked (recaptured) specimens. The Schumacher-Eschmeyer estimator provided very close results between the summer (N = 212 and density = 2.8 ind./m2) and the winter (N = 218 and density = 2.9 ind./m2) estimates. The Schnabel estimate results were also very similar to that obtained by the Schumacher-Eschmeyer method for each corresponding season of the year. Regardless of the marking technique employed, the results obtained and field observations from each estimate indicate that none of the assumptions required by both methods were violated. After subtracting the percentage of immature specimens, the projected overall population size of mature Aegla franca for the whole extension of Barro Preto stream varied from approximately 33,200 in the summer and 29,500 adults in the winter (Schumacher-Eschmeyer estimator) for an estimated area of occupancy equivalent to 0.0125 km2.