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sharks made us very scared this summer, mainly for suspected attacks on humans. However, humans pose a greater threat to sharks than sharks to us.
The 34th Official Shark Week will take place from July 24 to July 30 on the Discovery Channel and aims to increase conversation and education about these ancient marine predators essential to ocean health. (Discovery Channel and CNN share parent company Warner Bros. Discovery.)
There are more than 500 species of sharks. They are as diverse as the dwarf lantern shark, which is smaller than a human hand, and the whale shark, which can grow as long as a school bus, said marine biologist Michael Heithaus, professor and dean of the College of Arts, Sciences & Education at Florida International. University at Miami. Since there are a large number of unique species, some characteristics may be true for one species but not another.
Sharks have been around for hundreds of millions of years, and as they continue to evolve, they are also in grave danger. Largely due to overfishing, shark and ray populations declined by 71.1% between 1970 and 2018, according to a 2021 study published in the journal Nature.
Sharks have one of the longest life spans compared to other animals.
Greenland sharks are the longest-lived known vertebrate on Earth, according to a 2016 study published in the journal Science. Researchers using radiocarbon dating have determined that the North Atlantic species likely lives an average of at least 272 years, often maturing only at 150 years of age.
Greenland sharks can live for at least 400 years, scientists estimate.
The earliest evidence of shark fossils dates back to 450 million years, meaning these creatures existed at least 90 million years before trees and 190 million years before dinosaurs.
Sharks have been around since Pangea fell apart, said Catherine Macdonald, director of Field School and a teacher at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science. (There was one giant continent called Pangea about 250 million years ago.)
In addition, sharks have survived five mass extinctions, one of which wiped out about 96% of all marine life.
Tiger sharks, one of Australia’s main predators, can help ecosystems respond to extreme climate events. The species’ prey, which includes green turtles, seabirds, and stingrays, avoid shallow water, often areas of seagrass. As a result, the seagrass can become shrubby, creating a safe haven for juvenile fish, shrimp and crabs, Heithaus said.
Seagrass absorbs the carbon in the atmosphere and uses it to build its body. When the seagrass dies, the dead material is buried in sediment on the ocean floor and the carbon is taken out of circulation, Heithaus added.
Researchers are currently trying to determine whether this phenomenon also occurs in other shark species and in other places such as coral reefs.
“It looks like it’s more than just tiger sharks,” Heithaus said. “It’s probably these larger species that play an inordinate role in shaping the ecosystems they’re a part of.”
Shark reproduction patterns vary.
On average, sharks give birth after 11 or 12 months of pregnancy, but some sharks, such as the frilled shark and basking shark, can be more than three years pregnant.
Some sharks, such as mako sharks and bull sharks, give birth alive, while other sharks, such as cat sharks, lay eggs, said Jasmin Graham, president and CEO of Minorities in Shark Sciences, based in Bradenton, Florida.
Long pregnancy terms and the fact that some sharks take 10 to 12 years to reach sexual maturity, such as the great white, are further impacting populations decimated by unsustainable fishing practices.
Sharks are mainly silent creatures, as they have no organs to produce sound.
Instead of talking, sharks communicate through body language, such as zigzagging, shaking and moving their jaws.
Sharks have a sixth sense: they can pick up nanoscopic electromagnetic currents. This extra sense can help them navigate the ocean and find prey or even a mate.
“The minute electrical impulse that a prey’s brain sends to its heart to make it beat is detectable to sharks, so they can find the hidden prey quite effectively,” Macdonald said.
With this finely tuned sense, sharks prey on sick and weak animals and play a vital role in keeping the marine ecosystem healthy.