Cownose Rays Galore!

I was walking over the Melbourne Bridge the other day scanning the Indian River below. I expected to see dolphins, osprey with fish in their talons, diving pelicans, maybe a manatee. I didn’t expect to see hundreds and hundreds of rays swimming beneath me. In many years of looking, this is something I’d never seen before. I had to find out more.

The Smithsonian Field Station in Fort Pierce has an excellent data base of animals found in the Indian River, complete with descriptions and pictures. The rays’ square snout and pointy wings, or pectoral fins, along with the fact that they were swimming near the surface in an enormous school, rather than hovering over the bottom in ones and twos, pointed to the cownose ray, or Rhinoptera bonasus.

The cownose ray is one of fifteen species of elasmobranchs (fish with cartilaginous skeletons, includes rays, skates and sharks) in the Indian River lagoon. Their dorsal surface, or back, is brownish to better blend in with the lagoon bottom when seen from above, and their white ventral surface, or belly, blends in with the bright sky when seen from below. Cownose rays are bottom feeders. They stir up the lagoon bottom with their pectoral fins, then suck up sediment with worms, crustaceans, fish and mollusks through their small, ventral mouth. They send water and the inedible bits out through their gills and eat the rest. Cownose rays, in turn, are eaten by bull sharks, sandbar sharks and cobia.

Cownose rays were said to travel through the Indian River between August and November, but it was definitely June when they were traveling under Melbourne’s bridge, so I asked the experts why.

Dr. Gavin Naylor, who heads the Florida Program for Shark Research, said there seem to be two species these days in the Indian River: Rhinoptera bonasus and its Brazilian cousin, Rhinoptera brasiliensis. The only way to distinguish one from the other is to examine their teeth, something that can’t be done without “sampling” the rays.

Dr. Grant Gilmore, who has been called Florida’s Foremost Fish Expert, was surprised to see such a large number of cownose rays here. Since these rays eat mollusks, he’s going to talk to the “clam people” to see if they have more information.

Dr. Matt Ajemian from Harbor Branch Oceanographic Institute is tagging and sampling cownose rays in the Indian River and plans to publish his findings soon. He told me of cownose ray killing contests in the Chesapeake Bay. Killing the rays, which migrate to the Chesapeake Bay each summer to give birth, was promoted in a cruel and misguided effort to boost dwindling oyster harvests. Dr. Ajemian has searched the stomach contents of many cownose rays and found very few oysters. The killing has been banned, which is good news for the ray. Though hundreds and thousands of cownose rays may be seen at one time, they are very slow to reproduce and repopulate. Cownose rays are several years old before they reach sexual maturity, and then females bear only one pup per year.

The more I learn about these Indian River cownose rays, the more questions I have. The scientists I spoke with thrive on questions. The Indian River cownose rays are like a puzzle and each new discovery adds to the picture of this species and its place in our environment.

Seeing an enormous school of rays is pretty special, and I felt obliged to share the sight with others. “Do you see the rays!” I asked a walker, pointing excitedly towards the water. “I do now” she answered curtly. Underwhelmed and miffed about the interruption, she put her earbuds back in and continued on. And this brings us, as BlueTube blog posts eventually do, to ocean plastic. If we don’t care about cownose rays, we will never care about plastic polluting the waters they swim through. Our oceans, lagoons, bays and rivers are full of really cool life that is worthy of enthusiasm and protection. How can we all help protect the Indian River and its amazing creatures? Grab a bag from the BlueTube on the shore, pick up trash and throw it away. Add clean, used bags to BlueTubes so others can keep plastic out of the water too. If your favorite stretch of shore doesn’t have a BlueTube, go ahead and sponsor one.