Food, Not Cuddles for Cuttlefish Babies
Previous Getting our “Sea Legs,” and Bound for South Georgia
Did you know that 14 different species of sharks have been found in B.C. waters? Some of them are visitors to our waters, but others call the Vancouver Aquarium home. This season, explore Vancouver Aquarium’s galleries to uncover the amazing lives of the not-so-famous sharks and their cousins – the skates, rays and ratfishes – in our new seasonal feature titled The Secret World of Sharks and Rays, which opened yesterday.
Sharks are incredible fishes with amazing adaptations that allow them to live very diverse lifestyles. Some famous ones, like the white sharks, are constantly on the move; other not-so-famous ones, like a tasselled wobbegong (Eucrossorhinus dasypogon), are sneaky and inconspicuous.
Rays, skates and ratfishes are cousins of sharks. They share similarities that put them in the same cartilaginous group of fishes called chondrichthyes (“cond-rik-thees”) – which means they’re all boneless.
As you may already know, sharks are excellent hunters. They have well-developed senses and body shapes that have evolved and adapted to hunt particular prey. For example, the tasselled wobbegong (Eucrossorhinus dasypogon) is shaped and coloured to have excellent camouflage allowing it to be a successful sit-and-wait predator. It also uses its electrical sense to find flatfishes and crabs buried under the sand, and its lateral line system (lines of pores along its body) help detect their prey’s movement.
Sharks have an incredible sense of smell. They can smell a tiny amount of their prey’s blood, hormones and amino acids, even when diluted with sea water.
Their eyes have reflectors (called tapetum lucidum) that act like mirrors and sharpen their vision in dim light. They’re sensitive to seeing movements in the dark.
Sharks hunt silently. The secret? Teeth on their skin. When seen under a microscope, their skin looks like they have tiny spines or “teeth,” called dermal denticles. Dermal denticles allow sharks to swim stealthily by cutting down the sound of their movement. They also help sharks swim faster with less energy by reducing drag and turbulence.
Sharks have amazing teeth. They have lots of them and they are easily replaceable. They are unique to each species of shark, and experts can generally tell what a shark eats by the shape of their teeth. The whitespotted bamboo shark (Chiloscyllium plagiosum), for example, is a generalist feeder and has the teeth to show for it. They are shaped not only to snag soft-bodied prey easily, but can also fold down to form a plate and crush a crab or shrimp.
Rays, such as stingrays, are sharks’ cousins. These boneless predators also have keen senses and well-adapted bodies.
Like sharks, ray teeth are also shaped differently depending on the type of food they eat. For example, the brown stingray (Dasyatis lata) has the same teeth shape as whitespotted bamboo sharks (Chiloscyllium plagiosum) – rows of small, spiky teeth, prefect for clutching soft-bodied prey, with the ability to fold down for crushing hard-shelled ones.
However, unlike most sharks, rays don’t use their sight to hunt. They can’t see what’s beneath their flattened bodies, where most of their prey hide. Scientists think rays use their vision to spot predators and mates instead. Their crescent-shaped eyes give rays a larger visual field to see their surroundings.