Researchers working off the coast of Baja California in Mexico have captured stunning video of a "fish tornado" swirling underwater. The imagery is so unusual many viewers have asked if it's real or fake. (Answer: It's real.)

The brief video shows a large school of jack fish (family Carangidae) engaged in a kind of courtship behavior called a fish aggregation. "I have been trying to capture this image ever since I saw the behavior of these fish and witnessed the incredible tornado that they form during courtship," marine biologist Octavio Aburto told Mission Blue.

The footage was taken in Cabo Pulmo National Park, a marine reserve that's teeming with sea life. Aburto and another researcher "had to stay in the water for almost an hour before we started photographing. We ended up swimming all over the place following the fish and waiting for them to start performing the courtship behavior."

Affiliated with the Scripps Institution of Oceanography near San Diego, Calif., Aburto has been working in Cabo Pulmo for 15 years. He hopes to use his underwater photography "to raise awareness about what is happening in this beautiful national marine park, as well as bring attention to other successful marine reserves, especially in Latin America."

Follow LiveScience on Twitter @livescience. We're also on Facebook & Google+.