Batoids

[dropcap]M[/dropcap]y first article for Coastal Angler was about seabirds, the avian kind. But this past month as I watched a father and son marvel at the beauty of the stingrays in our touch tank the young boy blurted out that they are seabirds. What he saw were magnificent swimmers that as they glide through the water with their greatly enlarged pectoral fins resemble graceful birds of the ocean – it was a beautiful analogy coming from the mouth of a babe. For the most part, it is the eagle, cownose, manta and devil rays that are the embodiment of winged flight as they are the strong swimmers of mid-water, occasionally even jumping out of the water into the air. The accepted common name for the cartilaginous group that includes not only stingrays, mantas and skates but guitarfish as well are batoids, picking up not so much on their graceful movements but more so on the flapping of their wide fins.

Found in every ocean but the Southern Ocean, they most often inhabit shallow temperate and tropical waters. A little less than ten percent of the species can be found in fresh water and the manta rays represent the few that forage in the open ocean. Some of the most beautiful descriptions of these sleek fish are linked to their seasonal migrations. The cownose rays are known to migrate from the Yucatan to Florida in the spring as well as up the east coast of North America. Similarly they migrate west and south again in the fall. Many years back I was privileged to witness a northern migration of the beautiful spotted eagle rays as they were traveling north just offshore central Florida in early February. The fever, as a school of rays is called, was an average of five animals wide and stretched for at least two miles.

Although most people who have up-close and personal encounters with rays in the wild hardly remember their soft skin, it can truly be described as being as soft as “chamois leather” or even “a wet mushroom”. My own encounter happened at Fort Pierce Inlet in central Florida. I was not doing the “stingray shuffle” which alerts them to our presence and usually hastens them along. When I stepped on it, its skin was exceptionally soft and I thanked my lucky stars that its venomous barb didn’t hit its mark. Oftentimes the encounter happens when a ray is caught on hook and line when using a de-hooker would really help. The sting is painful and folks that regularly spend time in our coastal waters pack pocket warmers in their first aid kits just in case, knowing that heat breaks down the protein of the venom. A follow-up at the doctor’s is imperative because the barb can harbor nasty infections.

To many the barb is a mystery. If they have no bones, only cartilage, what exactly is the structure that pierces so effectively? As it turns out, it is technically a fish scale. Sharks and batoids have unique scales called placoid scales that more closely resemble teeth because they are covered with enamel. Their toughness protects the fish against predation and their keeled shape also reduces turbulence as they glide through the water. The barb of the stingray is actually a modified placoid scale that is elongated, frequently has serrate edges and has a venom gland at the base. Its primary purpose is not to harm humans – rays have been around a lot longer than we have – but rather as defense against aquatic predators. Since they are bottom feeders, they are most often attacked from above when a predator tries to pin them down. One quick flick of their tail and they can inject the painful venom and hopefully ward off the attack.

If it seems like the rays have done more than their share of adapting, you are right. It is likely that the common ancestor of batoids was a fish not too much unlike a guitarfish, the likely link between the pelagic sharks of the Jurassic period and the bottom dwelling rays that we know today. Besides the wide pectoral fins and the modified scale for self-defense there is one other key adaptation, the spiracle. Sharks take oxygenated water in their mouth, pass it over their gills and then out their gill slits. But rays that spend much of their time on the bottom where their mouth is located for feeding have a spiracle, a modified gill slit on their topside, usually behind their eye that draws oxygenated water in that is directed out the gill slits on the bottom side. This keeps bottom sediments out of their gills while at the same time exposing buried food like clams and other invertebrates.

If I have intrigued you enough to get over your stingray phobia, I invite you to come out to our Coastal Center to spend an enlightening day with our rays that have been de-barbed. You may come away appreciating this fish more than you ever thought possible.