MYSTERIOUS monster sharks that outlived the dinosaurs have been found lurking in waters just 20ft deep off the US coast.

The giant sixgill sharks have been spotted year-round in Washington State’s Puget Sound – despite the species usually living thousands of feet below the ocean surface.

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Giant sixgill sharks have been found in shallow waters off the US CoastCredit: Seattle Aquarium
 

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The crew at Seattle Aquarium made a special ‘cradle’ so they could safely and rapidly study the sharkCredit: Seattle Aquarium
Marine experts say the elusive beasts can grow up to 14ft long and have existed before dinosaurs roamed Earth.

The eerie predators, known scientifically as Bluntnose sixgill shark, are rarely seen because they normally dwell in deep ocean waters at depths of up to 9,800ft in extremely low-light conditions.

But researchers from Seattle Aquarium are now studying the sharks after discovering they appear to return to the Salish Sea repeatedly to give birth.

Scientists believe the waters of Puget Sound act as a nursery for baby sharks, known as pups.

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The young sharks spend summer and fall in the southern parts of the Salish Sea before moving north during winter and spring.

Researchers say the creatures usually travel less than two miles a day and rise into shallow waters at dusk before descending again at dawn, likely while hunting prey.

“We think these patterns repeat until they eventually depart for the open ocean,” Seattle Aquarium said in a statement.

“This consistency of movement and behavior reinforces the strength of our opportunity to study sixgill sharks in Puget Sound.”

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Aerial view of Puget Sound, Seattle, Washington
The sixgill sharks, which predate dinosaurs, have been seen lurking in waters just 20ft deep in Puget SoundCredit: Getty
 

A huge public display of water creatures in Seattle, Washington
Researchers from Seattle Aquarium are studying these sharks, believing Puget Sound serves as a nursery for their youngCredit: Getty
“Through our research, we hope to answer questions about the life history and ecology of sixgill sharks—including migration, growth rates and prey preferences,” they added.

Unlike most sharks, which have five gill slits on each side, sixgills have six – giving the mysterious species its name.

From May to September, aquarium researchers and vets will visit three locations in Puget Sound once a month to study the creatures.

The team plans to lift the sharks to the surface, either bringing them onboard or holding them beside the boat before flipping them upside down to trigger a trance-like state used in several shark species.

Scientists will then collect measurements, tissue samples and photos before fitting the animals with wearable tracking tags.

The process takes just five to 10 minutes before the sharks are released back into the water.

The tags are expected to reveal more about the animals’ movements, feeding habits and habitat use.

“Our goal is to answer as many questions as possible,” Dani Escontrela, a researcher at the Seattle Aquarium, said in the statement.

“We’re collaborating with agencies like the Washington Department of Fish & Wildlife, the Big Fish Lab at Oregon State University, Point Defiance Zoo & Aquarium and other researchers to fill gaps in expertise, all while keeping animal health and well-being our top priority.”

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The beasts can grow up to 14ft long and usually live thousands of feet below the ocean surfaceCredit: Seattle Aquarium