This vast expanse of magnificent stingrays animates the bright blue seas of the Gulf of Mexico.
Taken off the coast of Mexico's Holbox Island by amateur photographer Sandra Critelli, this breathtaking picture captures the migration of thousands of rays as they follow the clockwise current from Mexico's Yucatan peninsula to western Florida.
Measuring up to 6ft 6in across, poisonous golden cow-nose rays migrate in groups - or 'fevers' - of up to 10,000 as they glide their way silently towards their summer feeding grounds.
They migrate twice yearly: north in late spring (as pictured here) and south in late autumn.
There are around 70 species of stingray in the world's oceans, but these cow-nose rays (Rhinoptera bonasus) have distinctive, highdomed heads, giving them a curiously bovine appearance.
But despite their placid looks, they are still armed with a poisonous stinger, which can be deadly to humans (even though sharks, their main predators, are more likely to provoke them).
The stinger, a razor-sharp spine that grows from the creature's whip-like tail, can reach almost 15 inches in length and carries a heady dose of venom.
But even equipped with this powerful punch, cow-nose stingrays are shy and non-threatening in large 'fevers'. Even when isolated, they will attack only when cornered or threatened.
They migrate long distances, and can be found as far south as the Caribbean and as far north as New England.
They use their extended pectoral fins to swim, and often turn upside down, curling their fin tips above the surface of the water - leaving terrified swimmers convinced that they have seen a shark.
Their flexible fins also come in handy when rustling up food. By flapping them rapidly over the seabed, they stir up sand and reveal crabs, shellfish and oysters, which they then feed on using their powerful, grinding teeth.
Their numbers are exploding, thanks in part to rising sea temperatures. They mate every winter, and females produce a litter of five to ten young.
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