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Existing on earth for more than 400 million years, sharks have learned how to survive natural disasters and mass extinction events by diving deep into oceans and predicting storms. Along with volcanic eruptions, tornadoes and hurricanes, they have also survived the Big Five – the series of mass destruction events that destroyed swathes of plants and animals over millions of years.
Image Credits: Pixabay
The most disastrous of them was the Permian-Triassic extinction also known as the Great Dying, which occurred 252 million years ago. This mass extinction event destroyed 90 percent of marine life, 70 percent of land wildlife from which the Earth took 10 million years to recover.
However, sharks survived.
Finding Evidence For Shark Life In Deep Water
According to the research published in 2013, during the Cretaceous period (a geological period that lasted about 145 to 66 million years ago), palaeontologists (people who study fossils) found fossilised teeth of the tiny Cladodontomorph shark. Researchers had previously thought that this shark was the victim of the Great Dying. But new data shows it survived by diving deep into the water. Modern sharks still have this inborn instinct. Researchers at the Center for Shark Research (CSR) at Mote Marine Laboratory, U.S., observed that all 13 juvenile blacktip sharks left the shallows of their nursery in Terra Ceia Bay, Florida, and departed before Tropical Storm Gabrielle occurred in 2001.
Natural disasters have many intense effects on the waters and marine lives they hit. Storms can create desalination, remove minerals or salts, decrease oxygen levels and cause anoxia (lack of oxygen in tissues). They can also damage the seabeds and reefs, increase run-off contamination from the shore and cause pollution from washing debris into the sea. Additionally, disasters can harm sharks by hitting with high-velocity water currents and winds.
According to a Florida International University (FIU) study of juvenile bull sharks during Hurricane Irma 2017, shifting from nearshore areas could mean the difference between the life and death of sharks. They assumed that three young sharks were killed, remaining in the shallows for a longer period.
As per another study at the University of Miami, U.S., great hammered, bull and nurse sharks also went to deeper waters during Hurricane Irma 2017. Researchers believed two nurse sharks took refuge in coral ledges as they left the shallow waters of the Biscayne Bay for safer and deeper waters to prevent themselves from lower oxygen and saline levels and surface chop.
Prevailing The Disaster
Sharks know to leave before the storm arrives. The “highly directed movement out of the bay, synchronicity of departures, and narrow time frame of the phenomenon indicate this change in behaviour was a response to an environmental cue associated with the storm,” according to the CSR in the Journal of Fish Biology.
The University of Massachusetts Amherst, U.S., discovered that Caribbean reef, lemon, nurse and tiger sharks left the area two hours before Hurricane Maria arrived in 2017. The FIU study also showed that the three bull sharks left a week ahead of the storm.
By studying the survival behaviour of modern sharks, researchers could explain how their ancestors survived. The CSR observed the environmental factors of Tropical Storm Gabrielle and discovered that the amount of wind speed, rainfall and tidal made a slight difference. The wind speeds were not as high as the area had experienced before. Also, salinity had not declined to the levels that were uncomfortable.
According to a study at Aberdeen University, UK, the drop in the barometric pressure provided a warning. Sharks were able to detect this using their vestibular hair cells in the inner ear and sensory organ called the lateral line. The research showed that it only takes 0.005 bar pressure decrease for the sharks to react and respond to the change in 10 seconds.
Sharks can use warning systems to live in the surroundings of submarine volcanoes. Besides detecting barometric pressure, they can also detect the Earth’s tectonic or magnetic field movements.
“They might sense vibrations in the water or detect some of the sounds that come before an eruption,” explained Michael Heithaus of FIU.
Capitalizing On Apocalypse
Not all sharks have the same responses to disasters. According to the University of Miami’s study, tiger sharks survived Hurricane Mathew 2016, and their number doubled in the immediate aftermath.
“It was as if they didn’t even flinch,” said Neil Hammerschlag, a Research Associate Professor at the University of Miami and the study’s co-author. He believed that the plenty of post-storm fatalities attracted the sharks to stay. These sharks adapted to the dangers of the storm and flourished in its consequences.
Some species of sharks returned to the shallows after the end of the Permian mass extinction, while other species got adapted to deeper waters, concluded the Cladodontomorh study.
A team of volcanologists (people who study and monitor the Earth’s volcanoes) studied the active Kavachi volcano near the Solomon Islands and recorded that silky and scalloped hammerhead sharks have adapted to boiling and toxic waters.
In the catastrophic world of the Big Five, the sharks have survived due to their ability to adapt to the acidic, darkened and deoxygenated waters.
Now, sharks will face their sixth mass extinction event called Holocene. Human activities will be responsible for this extinction event. This time, they will require more than their instincts to save themselves or else they will not be able to survive.
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