Gliding silently under the seas these magnificent stingrays resemble a golden cloud stirring in the ocean.
Taken off the coast of Holbox Island in Mexico in July last year these spectacular pictures show the twice yearly migration of thousands of cow-nosed stingrays.
Sandra Critelli, an amateur photographer, came across the phenomenon whilst on a whale shark expedition with the Shark Research Expeditions of Philadelphia, on the northern tip of the Jucatan Peninsula in the Gulf of Mexico.
Magical: Golden Rays migrating in the Gulf of Mexico
But upon seeing these leaf-like animals, her attentions were quickly switched to the school of fish commonly known as Golden Rays.
"It was an unreal image, very difficult to describe," says the 41-year-old from Linden, New Jersey.
"The surface of the water covered by warm and different shades of gold, looked like a bed of fall leaves, gently moved by the wind .
"It was just unforgettable! I've never seen something like that, and I travelled a lot, in different parts of the world, and seen some incredible things.
"But the Golden Rays school will always have a special place in my heart."
Measuring up to 7ft from wing-tip to wing-tip, cow nose rays are known for their long migrations in large schools.
Arc: The rays, swimming in a long line, was spotted by amateur photographer Sandra Critelli
In the Atlantic Ocean, their migration is northward in the late spring and southward in the late autumn.
The population in the Gulf of Mexico migrates in schools of as many as 10,000 rays, clockwise from western Florida to the Yucatan in Mexico.
Cow nose rays have a unique feature - long, pointed pectoral fins that separate into two lobes in front of their high-domed heads.
A crease in the lobes and a notched head create a cow-nose likeness that gives these rays their name.
Despite having poisonous stingers cow-nosed stingrays are known to be shy and non-threatening when in large schools.
And so it proved for Sandra, a textile designer by trade, and her colleagues who witnessed the near silent migration on the calm seas.
Close up: The rays, properly known as Cow-nosed Stingrays, are known because of their bovine-like high-domed heads
"Its hard to say exactly how many there were, but in the range of a few thousands," she reveals.
"We were surrounded by them without seeing the edge of the school, and we could see many under the water surface too.
"I spotted them on our way to the area where we planned to snorkel with Whale Sharks.
"The captain turned the boat in the directions of the Rays and turn the engine off when we got closer.
"In a few second the Rays were all the way around us , we observe them, took pictures and just enjoyed the wonderful scene, for a few minutes, 10-15 minutes, following them very slow and gently.
"When the Rays start moving faster and away from us , we left.
Stunning: Onlookers watch as thousands of Golden rays make their migration in the Gulf of Mexico
"I have never seen anything like this before - it was spectacular and unforgettable experience."
After posting her images on the internet, Sandra has received many compliments for her spectacular images.
"So many people appreciated my Golden Rays images, I received a lot of compliments regarding them," she says.
"My expedition was about the Whale Sharks, but the Golden Rays seem to have got more attention.
"When I came back to town that day, the word spread quickly of the unusual event and I was asked to show my picture around.
"So many Golden Rays in that area have never being spotted before.
"I feel very fortunate I was there, in the right place at the right time , to experienced nature at his best !"
The great ocean migration... thousands of majestic stingrays swim to new seas | Mail Online