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Love them or hate them, you can’t deny that they are one of the most fascinating species on the planet. Many amazing facts about sharks are already commonly known, such as their ability to detect one part of blood in a million parts of water, or that their skeletons are made from cartilage instead of bone. Here we’ve listed five lesser known facts about these fantastic beasts.
1. Swim For Your Life! Or Not?
It’s a popular belief that sharks will drown if they stop moving. In reality most sharks don’t have to constantly swim to breathe or to stay alive. The majority of shark species use a process called buccal pumping, named after the cheek muscles they use to physically filter water into their mouths and over their gills, and can alternate periods of activity and rest. Other sharks, however, use ram ventilation which means they ventilate their gills by swimming very fast with their mouths open. Some sharks (tiger shark for example) can switch between buccal pumping and ram ventilation depending on how quickly they’re swimming. Other group of sharks (including great white, mako and whale sharks) are “obligate ram ventilators” – they’ve lost the ability, and the necessary anatomy, for buccal pumping, and instead can only respire using ram ventilation. For this group of sharks it is essential to keep swimming to stay alive. They would indeed die from lack of oxygen if they stopped moving.
2. The Heat Within
We often refer to sharks as “cold-blooded” and while it is an improper description of their personality, it is true when it comes to their biology. Nearly all fish are cold-blooded, so are most sharks: in other words their blood temperature is the same as the ambient temperature of the water. But not all sharks are created equal. A small group of sharks called the Laminids have evolved the ability to maintain an internal temperature that is higher than their environment. This ability makes the Lamnids not cold-blooded but instead endothermic (the term means “heat within). The family lamnidae include the infamous great white shark, mako, salmon, and porbeagle sharks. Pelagic tunas and billfish, like swordfish and marlin, are well known for this physical capability, and research has shown that even some species of thresher shark can do so as well.
3. Designed For Life In Salt Water
Most shark species can’t tolerate freshwater at all. It’s because of the metabolic costs of osmoregulation –having to maintain the right pressure by controlling water and salt concentrations in the body. In other words most sharks cannot survive in freshwater. But there is also a very unique shark – the Bull Shark – that evolved a tolerance for freshwater by developing the ability to restrict removal of salt from their bloodstream by the rectal gland. The gills and kidneys also help adjust the amount of salt going in and out. Bull sharks are regularly sighted in Lake Nicaragua (some of them even live there permanently) and have been reported 2,000 miles from the ocean in the Amazon River.
4. A Prehistoric Nightmare
Megalodon (Carcharocles megalodon) is the largest known shark that ever lived. At a magnificent maximum length of 59 feet (about 18 meters) this colossal being was not one to mess with. Luckily for us humans the megalodon went extinct about 2.6 million years ago, although some folks believe it’s still alive and well in the deep sea.
5. Sharks DO Get Cancer
A common shark myth is that they don’t get cancer. This is simply not true. Just like humans and the rest of the animal world, sharks suffer from bacterial infections, parasites, infectious disease and… cancer. Unfortunately this myth has led to the slaughter of millions of sharks for their cartilage. That, along with the demand for shark fins, are the major reasons more than 100 million sharks are killed every year.