Visual servoing of an underwater robotics arm for automatic sorting of crustaceans

Crustaceans aquaculture is a rapidly growing sector, and automatising specific tasks can contribute to increasing its economic return as well as its sustainability. In this paper, we present an autonomous robotic system for sorting crustaceans by size, applied to crayfish farming. The system was designed in close collaboration with a crayfish farming company following a systematic user-driven approach. It consists of a waterproof robotic arm with a custom caging gripper lodging a camera, and a vision system to detect crayfish and sort them by size. All aspects of system design are presented: from manipulator and gripper design and control, to the development of the vision system, and the system integration. The system is evaluated in a controlled laboratory environment using synthetic crayfish models, and in a tank with live crayfish on a farm. Our evaluation shows that the presented system is capable of recognizing and selecting crayfish based on their size, and safely entrapping them in the caging gripper without causing any damage.