DESPITE their popularity, there is plenty of mystery surrounding the apex predators of the sea.

From the number of species to how they track their prey, sharks continue to surprise researchers with new puzzling traits.

For starters, researchers are still discovering new species of sharks despite already identifying over 400 different kinds.

"The deep ocean is so vast and we've spent so little time studying it, that it feels like every time a scientist goes out and does some fishing or trolling or even goes to a fish market in a little known place, they find a new species of shark," professor of marine biology Christopher Lowe told Live Science.

Sharks are so adaptable that scientists continue to uncover new kinds in a variety of habitats, especially in deep waters.

"Moreover, sharks can range greatly in size, from as small as a cigar (like the American pocket shark) to as large as a school bus (such as the whale shark," Live Science reported.

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Another mystery surrounding sharks is their strange migratory behaviors.

Scientists are not quite clear on how the predators swim around the vast and empty ocean without getting lost.

Great whites, for example, have been known to swim all the way across the Indian Ocean from the west coast of Australia to South Africa, a marine biologist said.

"It is an enduring mystery how sharks find their way through the ocean, which environmental cues they use, and how exactly those cues are detected and integrated," shark scientist Andrew Nosal told Live Science.

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While we don't know exactly how they migrate without getting lost, we do know that some sharks indeed migrate seasonally.

It's unclear how many species consistently migrate, but tracking studies show the tiger shark have "partial migration, where some individuals have a propensity to be homebodies and others have a propensity to migrate," Lowe said.

"And we don't know why."

Another endangered species of shark called Galeorhinus galeus have a three-year migration and return to its reproductive spot every third year, Live Science said.

However, it is still unclear why most sharks migrate and how they move through the ocean without getting lost.

When sharks aren't mysteriously traveling great distances, they are diving into deep waters for unknown reasons.

Trackers have documented the activity of many sharks, but when the fish dives to great depths it is hard to follow exactly what they're doing, said biologist Gregory Skomal.

"We have plenty of data on white sharks that shows that some of them go out to the middle of the Atlanta Ocean, wander around and dive down to depths as great as 3,000 feet every day," Skomal told Live Science.

"But we don't have any clue what they're actually doing there."

Skomal did say that they found some sharks in deep waters that appeared to be resting.

"I dare not say 'sleep' because it's hard for us to determine if and when these sharks sleep," Skomal said.

It is also unclear where exactly sharks fit in the underwater food chain.

The mysterious beasts are notoriously viewed as the apex predator of the ocean, but there are plenty of sharks that are actually prey.

"It's still a mystery exactly how sharks fit in," Nosal told Live Science.

"Surely they are important, and many species are indeed apex predators. But food webs are very complicated."

The effects that humanity has had on the ocean do not help our study of sharks either.

Many habitats have been disrupted through acts like overfishing, making their role in the ocean even more obscure.

The intelligence of sharks is also ambiguous.

While they don't have many folds in their forebrains which is the part associated with decision making and reasoning, they do have advanced development in their cerebellum which coordinates body movements, said biologist Jelle Atema.

One advanced aspect of sharks that is known is their sense of smell.

"In a 2010 study in the journal Current Biology, Atema and his colleagues found that dusky smooth-hound sharks turned toward odors stimulated first in their nares (nose), even if the second smell stimulation offered to them was higher in concentration," Live Science said.

This shows that sharks can focus on an odor plume even when another more concentrated smell appears in the busy ocean.

The predators also may have detailed memories about the time and location where they found food, Lowe said he observed.

Finally, scientists are still researching whether or not sharks are social creatures.

Some sharks have been known to gather together, but it is unclear whether this is due to the environmental conditions or attraction to one another.

"Almost certainly, it's going to be a combination of the two," Nosal told Live Science.

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"But we don't really know the extent to which sharks are social animals.

"There's more and more evidence that they are, but the details are forthcoming."

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