The optimal quadrat size for estimation of density of the golden apple snail, Pomacea canaliculata, in paddy field and comparison in usefulness between the quadrat, line transect and marking methods

摘要

Density of the golden apple snail, Pomacea canaliculata (LAMARCK), was estimated in a paddy field by the quadrat method using quadrats of four sizei: 0.5X0.5 m, 1X1 m 1.5X1.5 m, and 2X2 m. WIEGERT's and HENDRICKS' methods supported the quadrats of 2.0X2.0 m and that of 2.63 square metres as the optima, respectively. a line transect 2 m long and 0.3315 m wide and the JOLLY-SEBER marking method with traps were used to estimate snail density and their usefulness was compared with the quadrat method. The line transect method was more efficient than the quadrat method for the estimation of the density. The JOLLY-SEBER marking method provided estimates of snail density similar the quadrat method, but the 95 percent confidence intervals of the means for the former method were generally wider than those for the latter. It is suggested that the marking method can be substituted for the quadrat method, although the estimate will be conservative to some degree.