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:
Her account:
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:
I wondered how the ray actually manages to detect & manipulate its prey as it doesn’t seem to be able to see what’s going on on its underside. This video (youtube link) seems to be a fairly good angle to view it from, with some explanation below it in the text box.
Most fish in general (note these are chondrichthian jawed vertebrates ; you and I are more closely related to a cod than the cod is to the rays) have an electro-sensitive, errrr, sense working through their “lateral line” organ (I’m not sure that mammals have any remnants of this at all. “Help?, someone?”). That provides some degree of both distance and direction to [something with a different conductivity to seawater], and since it is picked up by sensors well-distributed over the body (literally, “nose to tail”), then it’s no great stretch to my imagination to envisage that the electrical disturbance from (say) a clam in the sand under the nose having a different “feel” to how the same clam “feels” when under the tail.
Most humans don’t have a sense that correlates to this. Perhaps a correlate would be the sense that some blind people develop for a personal sonar echoing from their walking noises back to their ears.
I would be surprised if they only used one sense in hunting for food. It is, after all, a rather important activity.
Very cool pics. I’ve sen these 2 or 3 at a time, but wow. Surely ‘school’ and not ‘herd’.
(and I can brook no criticism of Louis Armstrong, even implicit. The syrupy arrangement is fair game.)
A group of rays is apparently called a “fever.”
Ha, I was going to suggest, seeing rays at the surface, a “sunbath”. Which will give you fever if you do it much.
I was going to suggest “an inflammation of stingrays”.
I thought a group of rays was called a laser….
Only if they’re coherent!
Jerry knows the only reason I’m ‘redoubtable’ is that I’m on Twitter, where Ed Yong retweeted the first of these pics (which was taken at the latest in 2009 I think).
The photos are beautiful. I’ve seen a few of these at a time (Oregon Inlet, years ago) but didn’t know they congregated regularly in such large numbers.
Migration based on solar orientation makes sense to me – the ray’s flat shape and the school’s evenly-spaced orientation (near surface with nobody overlapping) suggests that the fish’s back is being used as a solar collector, perhaps as a way to estimate the sun’s position.
I have loved skates and rays since I was a small child, since we saw several species while vacationing on North Carolina’s Outer Banks each summer.
This is the first I’ve ever heard of this, it should be as well known as the migrations across the Serengeti, fabulous.
“Southbound migration has been observed to contain larger schools than the northbound migration.”
This is well-known too in ‘other things with wings’… birds and butterflies, for example. Mortality takes its toll on first-time migrants, both en route and during their early year(s). Many go; fewer return.
Looks like an Escher lithograph …
à la Metamorphosis III
That’s what I thought too. Maybe it should be an Escher of stingrays? 😉
I second the motion!
Beat me to it. Wonder if Esher ever saw anything like this?
Wonderful! An incredible sight!
What a lovely name – Rhinoptera = nose-wing!
bonasus = cow nose
That is awesome! Thanks for sharing.
I bet the people on that boat won’t ever forget that sight. Lucky so and so’s. 🙂
There are some classic “wallpaper” images in there.
However, I am compelled to keep the wife’s photo of a very dappled mountain streambed. And very nice it is too.
An “Escher” of rays. A nice idea, but it could too easily become an “Escher” of Moibus bands. And then no-one would know on which side to stand.
I’m sitting on my balcony watching the cownose rays go by. I revel every year in their migration. I’ve stood in the shallows and watched them swim around me; its an etherial feeling. We get groups up to perhaps 40 at a time; I can just imagine thousands coating the gulf at once. The exquisite beauty of nature is breathtaking.
And yes, Escher is one of the first associations that comes to mind!
Today I witnessed three schools of rays gliding past me within a one hour period, as I watched from Charlie’s Pasture in Port Aransas Texas. Took photos and wondered since we are expecting a cold front this weekend, that perhaps these cownose rays were aware of this change? A breathtaking sight that left me feeling so very lucky to live on an Island and witness these graceful beings glide through the channel, at least a hundred in each group.