Gliding silently beneath the waves, they turned vast areas of blue water to gold off the northern tip of the Yucatan Peninsula . Sandra Critelli, an amateur photographer, stumbled across the phenomenon while looking for whale sharks.
She said: 'It was an unreal image, very difficult to describe. The surface of the water was covered by warm and different shades of gold and looked like a bed of autumn leaves gently moved by the wind.
'It's hard to say exactly how many there were, but in the range of a few thousand'
'We were surrounded by them without seeing the edge of the school and we could see many under the water surface too. I feel very fortunate I was there in the right place at the right time to experience nature at its best' Measuring up to 7ft (2.1 meters) from wing-tip to wing-tip, Golden rays are also more prosaically known as cow nose rays.
They have long, pointed pectoral fins that separate into two lobes in front of their high-domed heads and give them a cow-like appearance. Despite having poisonous stingers, they are known to be shy and non-threatening when in large schools.