Effect of two collapsible pot designs on escape rate and behavior of the invasive swimming crabs Charybdis japonica and Portunus pelagicus

Escape rates and behaviors of the invasive crabs Charybdis japonica and Portunus pelagicus were investigated in two commercial pots: a box-shaped pot with two slit entrances at the ends and a dome-shaped pot with two open funnels. A variation of the dome-shaped type with two plastic triggers installed in each entrance that served as non-return devices was also tested. Pots, each with one marked crab inside, were set in a pond that is connected to Kagoshima Bay, Japan. Escape rates over a 7-day period were observed while diving. Furthermore, escape behaviors of C. japonica were examined in a tank for both types of pots containing a single crab in each. Escape rates of crabs were highest in the dome-shaped pots because of the open funnel entrances, followed by those in pots with triggers installed, but there was no escape in the box-shaped pots because the tight slit entrances prevented the crabs from getting out.