Energy associated with ocean currents can be captured, just like wind currents can with wind turbines. Ocean turbines can be fixed to the seabed, or float nearer the surface with moorings attached to the seafloor. No one technology has yet emerged as a clear winner, but this Japanese turbine, which has been in development and testing for many years is clearly still in the race. After successful recent trials, the company is set to scale up to a 2 megawatt unit.
https://www.sciencealert.com/japan-s-dropping-a-kaiju-sized-turbine-into-the-ocean-to-fish-for-limitless-energy