Researchers tagging tiger sharks off the southern coast of Belize couldn't believe their eyes when they recently reeled in a different kind of fish.

It turned out to be a Greenland shark, which is typically found in the Arctic and can live to be over 500 years old.

The team of scientists thought the shark was dead when they finally hauled it to the surface.

Unlike the tiger sharks they were after, this particular shark had black, worn-looking skin and pale blue eyes.

Devanshi Kasana, a Ph.D. candidate at the Florida International University Predator Ecology and Conservation lab, said the shark looked "really, really old."

"It was just very surprising and confusing," she said.

"As soon as it entered our field of vision, we saw a black figure that was getting bigger and bigger.

When it came to the surface, none of the crew with all of their combined fishing experience had seen anything like that."