Trap efficiency assessment using the size-class DeLury method in an eradication project for the invasive crayfish Pacifastacus leniusculus in a small pond

A project to eradicate the invasive crayfish Pacifastacus leniusculus was conducted from 2008 to 2012 at a small pond with a surface area of approximately 820 m2 in Kushiro. However, we could not eradicate it using Kanikago traps. To determine the reason, we examined the data for 2008 and classified the crayfish by body size and applied the DeLury method to each size class. A population decline was observed in large adults with carapace lengths of 4 cm or more, but not in small adults with carapace lengths of less than 4 cm. This revealed that the Kanikago traps were effective for large adults, but not small adults.