Have you ever heard the term ‘elasmobranch’ and wondered – what kind of animal exactly is that?
Here’s your answer:
Elasmobranchs are a subclass of cartilaginous fish; in other words they have a skeleton that is made of cartilage instead of bone. The Subclass is made up of roughly 1150 different species of sharks, rays and skates containing a wide range of shapes, sizes and colours.
Other defining characteristics of this subclass are:
- Unlike most bony fish, these animals don’t have a swim bladder, instead their livers are full of buoyant oil.
- They have between 5 and 7 gill slits on each side of their head.
- Bony fish skulls are rigid and only the bottom jaw can move, whereas an elasmobranch’s top jaw isn’t fused to their skeleton allowing the whole jaw to move.
- Their jaws are full of multiple rows of teeth that are continuously replaced.
- Their scales are also different from other fish: they are called placoid scales and are covered in a hard layer of enamel making them extremely rough, like sandpaper.
Sharks are different to rays and skates mostly in shape and size. Sharks have a more three dimensional body and have evolved for life in the water column.
They swim by moving their large tail fin from side to side and have a rigid dorsal fin that is attached to a cartilaginous spine. Sharks tend to eat by tearing and ripping flesh with their powerful jaws and sharp teeth, and have a large size range, from the dwarf lanternshark (max. 20cm) all the way to the whale shark (max. 18m). They reproduce by giving birth to live young or laying eggs (known as mermaid’s purses), depending on the species.
Rays have a flattened body and have evolved for life on the seafloor (although there are species of freshwater rays!) They differ from sharks in a variety of ways, most notably the shape and lack of dorsal fin. They swim by flapping their extended pectoral fins, or wings, and gliding through the water. Rays also range greatly in size, the smallest known ray species is the short-nose electric ray (max. width 10cm) whereas the largest is the giant oceanic manta ray (max. width 7m, max. weight 1500kg). All ray species give birth to live young. Instead of large teeth and powerful jaws they have plate-like teeth for crushing hard shells, rays also use their barbed tails, of which the barbed spines can be venomous for defense and hunting. There are also species of electric ray that can produce a voltage ranging from 8-220 volts to stun prey or in defense.
Skates are very similar to rays however there are some important differences. I like to think of them as the halfway point between sharks. They have a flattened body and live on the seafloor, like rays, however they have a prominent dorsal fin, like sharks. Skates swim similarly to rays however some possess tail fins that can also propel them through them forwards. Their tails do not have spines like rays however some species have protective thorn-like growths along their backs. Skates also differ to rays in their reproductive tendencies, they lay eggs, like sharks. The size range for skates isn’t as large as in sharks and rays, the smallest known skate specie is the little skate (max. 50cm) and the largest being the common skate (or blue skate) (max. 2.8m).
Common threats to Elasmobranchs
Unfortunately, as we all know too well, a lot of ocean-dwelling animals are threatened by humans, some to such an extent that future generations may never have the chance to see them. This is also the case for many elasmobranch species.
So many species of sharks, for example great whites, scalloped hammerheads and whale sharks, are severely endangered, be that through overfishing, bycatch or simply colliding with large vessels. Unfortunately shark fin soup is still widely consumed and the cartilage is used in traditional Chinese medicine and as an aphrodisiac in Japan. The scalloped hammerhead has seen a 95% decline in its population over the last 30 years and there are only 3500 great whites left. Most rays and skates are caught accidentally as bycatch. However certain species like sawfish are caught for sport and of the 5 different species, 3 are critically endangered (the other 2 are “only” endangered!)
Although many of the species under the subclass elasmobranch are threatened, a variety of different steps are being taken to successfully save these animals. This doesn’t prevent bycatch or even the illegal trade of them but it does help. The great white shark is fully protected but they are still under extreme threat from commercial fishermen, as bycatch in nets and on longlines. Other protected but threatened species include sawfish, whale sharks, manta rays and basking sharks.