Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Angel sharks and wobbegongs use camouflage to lie in wait and suck prey into their mouths. Teeth in these species are comparatively small because they are not needed for feeding. There was only one shark attack fatality in 2018. While some are small, others, like the whale shark, can grow up to 40 feet long. A Few Short Lessons About Sharks for Shark Week This week is Discovery's annual Shark Week. WWF supports research and monitoring of white sharks as they migrate to and from the Gulf of California. Tuna purse-seiners also catch sharks, although these have a better chance of being released alive, while gill nets are an ecological disaster, catching almost anything in their path, including whales, dolphins, turtles and sharks. But the IUCN Red List still identifies the species as “data deficient,” meaning its extinction risk hasn’t been fully assessed on a global level. At that point in Earth's history these rocks made up the soft bottom sediments of a large, shallow ocean, which stretched across much of North America. But it may have been even longer ago because unlike other fish, sharks have a flexible cartilage skeleton that is rarely preserved the same way typical fish bones are. Shark fin has become a major trade within black markets all over the world. Humans perceive sharks as a threat, yet the fishing industry kills up to 100 million sharks a year just for their dorsal fins. Preservation requires rapid burial in bottom sediments. So the next time someone calls you big mouth, think about a shark’s mouth and its ability to hold 300 rows of teeth with hundreds of teeth in each row, then look at them knowing they are fortunate that your mouth is actually quite small compared to a shark. Sharks have been known to get cancer. The researchers examined vertebrae from 17 sharks caught in the 1980s and in the past couple of years to determine their elemental compositions. Until recently, only a few benthic species of shark, such as hornsharks, leopard sharks and catsharks, had survived in aquarium conditions for a year or more. Other sharks are turning out to be older than researchers thought as well. Sharks can travel 70 to 80 km in a day. Few species have thrived on our planet for as long — and fewer have been so misunderstood. Researchers in Australia found a tumor protruding from the mouth of a great white shark in 2013. That’s not the case … It’s not true of all species, but great white, tiger, and mako sharks all need to keep moving in order to breathe. In most species, teeth are replaced one at a time as opposed to the simultaneous replacement of an entire row, which is observed in the cookiecutter shark. The evidence that sharks are at least resistant to cancer and disease is mostly anecdotal and there have been few, if any, scientific or statistical studies that show sharks to have heightened immunity to disease. Few governments enforce laws that protect them. Scientists determine their ages by studying layers of eye tissue, and they estimate that these sharks might not reach sexual maturity until they’re 150 years old.

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