Underwater harvesting system

An underwater harvesting system for harvesting zooplankton while towing, comprising: an underwater vehicle for (2) being lowered into the sea and towed behind a surface vessel (3), comprising a housing provided with an inlet (22) that is variable in size, through which zooplankton-containing-fluid may flow, a hose (4) mounted on the underwater vehicle and in fluid communication with the inlet, the hose adapted to secure and fluidly connect the underwater vehicle to the surface vessel, and pumping means to draw zooplankton-containing-fluid through the inlet and pump it through the hose to the surface vessel. The underwater vehicle further comprises a source of light (6) for emitting light with a predefined wavelength onto a defined water area (7) to facilitate schooling of zooplankton in the illuminated water area. The variable inlet size reduces the drag of the underwater vehicle when towing it through the ocean in search of zooplankton and, when a school is identified, the inlet is opened to increase the reach of the device and improve the catching effect.