TriplePundit points us to an underwater energy generator that feeds off the currents in the water as they push past its shark-like tail. The BioStream was designed by BioPower systems after studying the efficiency of shark tail fins. Their website explains:
The tidal power conversion system, bioSTREAM™, is based on the highly efficient propulsion of Thunniform mode swimming species, such as shark, tuna, and mackerel.
The bioSTREAM™ mimics the shape and motion characteristics of these species but is a fixed device in a moving stream. In this configuration the propulsion mechanism is reversed and the energy in the passing flow is used to drive the device motion against the resisting torque of an electrical generator.
Due to the single point of rotation, this device can align with the flow in any direction, and can assume a streamlined configuration to avoid excess loading in extreme conditions. Systems are being developed for 250kW, 500k.