Reef Report for Tuesday, September 19, 2006
Creatures of the Reef: Sting Rays
There are at 178 species of rays known worldwide, with many species found on the Great Barrier Reef. No doubt more species will be discovered as these animals are more fully studied. They range in adult size from smaller than a dinner plate to the colossal manta rays, which can grow to sizes over 6 metres (22 feet) across.
They are found in temperate to tropical waters ocean wide, as well as brackish water in estuaries and lagoons. Some species also spend their entire lives in fresh water rivers and lakes.
Most species of sting rays have one or more barbed spines (stings) at the base of their tail, which are used purely for defense, not to obtain food. There is venom-producing tissue surrounding the sting.
Sting rays, like sharks, are cartilaginous fish; they do have calcified bones but have a skeleton made of tough, somewhat flexible cartilage tissue. Many scientists consider sting rays as specialized sharks, not just related to sharks.
The flattened, pancaked body form or sting rays are an ideal shape for the bottom-dwelling existence that most sting rays lead. Some of the more well-known species, such as the manta and eagle rays, swim easily and gracefully, and lead their lives well above the ocean bottom, but the large majority of sting rays lead their lives quietly hidden on the ocean floor.
While much work on classification and anatomy has been done on stingrays, there has been little scientific work done on other aspects of their biology. Little is known about their feeding, migratory, or reproductive behavior.
The main food items of sting rays are varied. Most species feed on shellfish and other animals living on the ocean floor. Manta Rays are plankton feeders. At least one species, the Pelagic Ray, hunts and eats squid in the open ocean.
It is the sting of sting rays that is their most well known feature. The death of Steve Irwin was a rare accident, but worldwide there are a handful of deaths every year, and hundreds of people get stung each year. In the United States there around 1,500 incidents each year. Most stings are to the feet and lower legs, received when someone walking in shallow waters steps on a ray and triggers its defensive response. The second most common injuries are to the hands and arms of fisherman and other folks that are handling rays.
Most stings are painful, but heal without complications. The sting itself is thin and sharp in most species, with serrated edges much like a steak knife. These serrations make the sting very difficult to remove, most of the serious medical complications that come stings are due to the damage caused when the ray or victim pull the stinger out.
Unlike snake venoms, which are well-studied, not much is known about the venom of stingrays. The venoms studied seem to have three main components, one of which causes the immediate pain the victim feels, two other components cause tissue death. Without treatment the effects of the venom can continue for some time. Thankfully these venoms are very delicate molecules, and treatment by soaking the injury in hot water can break down the venom.
Stingrays are beautiful creatures, and are commonly seen by divers. One of the best dives we have done was off of Cayman Island in the Caribbean, at a dive site called stingray city, where thousands of divers each year go in the water with dozens and dozens of rays that come to be fed by hand.
When you visit the Great Barrier Reef you will probably see a ray, and if you keep in mind that they are capable of defending themselves if startled, and don’t approach them closely or handle them you will likely be very safe. Keep an eye out for smaller species on the sandy bottom and for the larger free-swimming eagle and bull rays, they are beautiful!
More Information about Sting Rays
How Stingrays Sting
Sting Ray City Dive Site
Biology of Rays and Sharks
First Aid Procedures for Sting Ray injuries
Other Creatures of the Great Barrier Reef
Crown of Thorns Starfish
Australian Snubfin Dolphin
Stout Infant fish (The world’s smallest fish)
The weekly reef report is written by Joel Groberg of DiveTheReef.com,
who compiles them from the many conversations he has with dive staff in the area, as well as many other local sources in the dive
Index of all reef reports.