In many areas, where they migrate upstream, crabs are caught in screens usually by dams and discarded. In many places, it is illegal to have or transport live mitten crabs. Bilge water in boats and ships must be carefully cleaned to avoid infesting other waters when the bilge water is released. Traveling screens have been placed in areas like dams when the mitten crabs are migrating in an attempt to capture them. In some places, commerical fishing of these crabs and exportation to Asia is encouraged as a method of control, because they are considered a delicacy there. However, they are very destructive due to their burrowing nature and attempts to control them have met with little success in both Europe and North America.