The redoubtable Matthew Cobb has called my attention to several posts on a phenomenon that’s new to me: a mass annual migration of stingrays—in this case the cownose ray Rhinoptera bonasus, found in the Atlantic and Caribbean. This species forages in groups, largely on clams and oysters. According to the Florida Museum of Natural History, their migrations also involve huge populations.
This pelagic species is also sometimes found in inshore waters. For the most part, this species is known for its migrations to different parts of the ocean (oceanodromous). The environments in which they are found include brackish and marine habitats. They are found at depths to 72 feet (22 m). They are gregarious and make long migrations. The cownose ray population is believed to be increasing in numbers. The migration patterns, in the Atlantic, include a northward movement in the late spring and southward movements in the late fall. Southbound migration has been observed to contain larger schools than the northbound migration. Smith and Merriner (1987) believe that the changes in water temperature, coupled with sun orientation, may initiate seasonal mass migration.
They also suggest that the southward migration might be influenced by solar orientation while the northward migration might be influenced by water temperature cooling below 22ºC, but further studies are needed to confirm this. The migratory congregation, thus far, has not been linked to feeding or premigratory mating activity.
One of these mass movements was witnessed by amateur photographer Sandra Critelli who, on Yacht Forums, described a migrating group (herd?) surrounding her boat and took some amazing photos:
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 whalesharks.
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’
The website adds:
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.
The population in the Gulf of Mexico migrates, in schools of as many as 10,000, clockwise from western Florida to the Yucatan .
Another photo by Critelli:
Here’s a swell photo from SuckMyHalo on tumblr:
And, from Environmental graffita, an image of a group of rays (cownoses?) and a whale shark:
A video of migrating cownoses (you’ll have to endure “Wonderful World” by Louis Armstrong unless you turn off the sound):
And, from the Virginia Institute of Marine Science, run by my own alma mater, The College of William & Mary, here’s a cownose in an aquarium eating oysters: