I am so stoked that I learned such awesome stuff in this little thing called a MOOC.
Confession: Despite being enrolled in the MOOC I had to Google what exactly the acronym stands for…wait for it…
Massive Open Online Course
I completed Sharks! Global Diversity, Biology and Conservation with Cornell University and the University of Queensland on the EdX platform and it was heaps of fun. (A little tricky, in places, I must admit, but nobody really expects Cornell to be a pushover, right?)
So here are ten cool things I learned about sharks.
- They are not bony fish, like the ones cats in cartoons eat. No, no. They are Chondrichthyans which means they have skeletons made of cartilage. There are three types of fish with cartilage skeletons : Sharks, Rays and Chimeras. (Chimeras are less like sharks than rays are.)
- A shark can stop swimming and survive for a time. Most sharks suction ventilate, ie, they suck in water by depressing the floor of their mouth and then force the water out over their gills.
- Rays are basically flat sharks with super duper pectoral fins. (I bet you never noticed that before, right? Take another look.)
- Sharks scales have similar anatomy to human teeth. (I kid you not. Dentine, enamel, pulp. The works.) They are called placoid scales or dermal denticles.
- A shark’s buoyancy is regulated by the high oil content of their livers. Throw a piece of cow’s liver into water and it sinks like an anvil. Shark’s liver bobs on the surface.
- Olfaction (smell) and hearing are sharks best long distance senses. You know that thing about sharks smelling blood from kilometers away? It’s true. They also hear pretty well, eg, the thrashing of a dying fish? They can hear that from more than a kilometer away. They use vision from about ten meters.
- Sharks have two extra senses that we don’t have, namely mechanosense and electrosense. They use these senses close up, unlike smell and hearing. Mechanosense is their ability to feel your movements. So if you are a dying fish and you thrash in the water, that moving water goes through little pores on the shark’s snout. The water flows into tubes where mechanosensory organs feel the vibes caused by the ripples.
- Electrosense is their ability to sense the electric field caused by the muscle contractions of their prey. They have electroreceptors on their snout and basically build a 3D model of the prey’s electric field. (The strange snouts of chimeras are covered in electroreceptors. It’s dark way down deep where they live so they rely on senses other than vision.) Electrosense is used close up, a meter or less. (Y’all have guessed how rays use their electrosense by now? Ever stood on an electric ray?) The next sense close to the prey will be touch, (the shark will bump it’s prey item), and the last sense, is taste. The bite.
- Sharks have a different shape lens in their eyes to humans so they can see clearly under water. Light refracts differently under water than it does through air, that is why we see blurs without goggles and sharks don’t.
- Be careful what you fish for. Commercial fishing, especially unregulated fishing in the high seas, and the demand for shark fin soup are decimating shark populations. So stop it already Shark finners. Enough. And a word to the recreational fisher, the catch and release boys. Sharks don’t recover well from the stress of the capture. The Sand Tiger, Carcharias taurus, or Ragged Tooth shark is particularly vulnerable. (Did you know raggies almost went extinct? Massive conservation efforts in the 90’s saved them. Which is cool because they’re pretty chilled and unlikely to bite you.)
There a zillion more cool things I could have shared with you. Sharks are amazing creatures, incredibly designed. The course has been archived now, but keep a look out for when it is rescheduled. It is worth the time and effort.
EdX is also an outstanding learning platform. Go see what they have that would interest you. The courses are free, the standard high and the subjects seem limitless.
COMING SOON on this blog: Massive Rant About Conserving Sharks. Although a MRACS doesn’t quite roll off the tongue like a MOOC ?