Autonomous vehicle for oyster aquaculture

Abstract

Marine aquaculture is a sustainable method for meeting the growing demand for seafood worldwide, filling the gap left by the stagnating volume of wild-caught seafood. However, compared to agriculture it has seen limited technological development over the past few decades [1][2]. The development and adoption of affordable technologies could greatly improve the productivity of marine aquafarms, benefiting farmers, consumers, and the environment. Our team worked with Ward Aquafarms, a local shellfish aquaculture company in Massachusetts, to understand where robotics and autonomous vehicles could help fill gaps in production efficiency. Ward Aquafarms uses the flip-bag method of oyster farming, in which large mesh bags are filled with baby oysters at the beginning of the growing season, strung together in a tight floating array, and periodically flipped. Flipping the bags is crucial to quality oyster growth, allowing each side to dry out and killing any growth on the mesh that would impede water flow to the oysters. Currently, Ward Aquafarms relies on a human farm worker to flip the thousands of bags on the farm. However, the manual labor required to flip these bags is slow and physically very difficult. The exertion required to lift the oyster bags repeatedly can cause strain and injury. Our solution is the Oystamaran, a catamaran with a linearly actuated flipping mechanism mounted between its two hulls, able to autonomously navigate down a row of bags and flip each one. Twin electric thrusters allow for both propulsion and steering, while an overhead camera and GPS provide feedback for precise positioning within the array. The flipping mechanism consists of an aluminum lever arm driven by a waterproof linear actuator and fitted with hook-shaped end effectors. The vessel straddles the working row and positions the next bag directly under the mechanism. Then the two hook-shaped end effectors scoop the far end of the bag, and the linear actuator retracts to mimic the action of a human worker. Rigid back stops push the bottom of the bag out from the frame and it slides back into place flipped over. Through testing in the lab and in the field, we demonstrated that the flipping mechanism reliably flipped oyster bags within the weight range expected on the farm. The vessel also successfully traversed a row of bags under radio control, able to smoothly move from one bag to the next. The first generation Oystamaran combines manual and autonomous navigation, allowing a shore- based operator to maneuver the vessel using radio control while the mechanism flips each bag. Further iterations aim to navigate to an array from a launch point, and traverse it fully autonomously. We are developing a computer vision system that allows the vessel to detect each row of bags as it approaches the array, and appropriately center each bag under the mechanism before flipping.