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Shark Week: Tiger Sharks May Yo-Yo Dive When Feeding
ByTo better understand tiger sharks' behavior, researchers attached accelerometers and digital cameras to the dorsal fins of four sharks
One of the ocean's top predators seems to maneuver through multiple sea columns to enhance hunting rather than save energy, according to recent research.
Tiger sharks (Galeocerdo cuvier) navigate vertically through water columns in what's called "yo-yo diving" -- or repeatedly descending into the ocean's depths and actively swimming upward in the same area.
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Before the data were collected, it was thought yo-yo diving in other fish might serve a purpose in conserving energy, perhaps assisting in regulating body temperatures or contributing to food foraging efforts. Energy conservation, in particular, makes sense at first glance since sharks can expend little energy by gliding during their descent into deeper waters and swimming back up.
But, as the study concludes, this wasn't the case.
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To better understand tiger sharks' diving behavior, researchers attached accelerometers and digital still cameras to the dorsal fins of four wild sharks for a total of 24 hours off the coast of Hawaii island. The equipment recorded the sharks' acceleration and angles of movement, which detailed their speeds and whether the animal traveled horizontally, vertically or a variation of both.
During the time scientists observed the tiger sharks, they discovered that all the animals practiced yo-yo diving. Though the sharks accelerated less while descending downward through the water columns, they didn't glide as predicted.
In fact, the sharks still accelerated while traveling downward through water columns -- a trend that coincided with the presence of potential prey items in photos recovered from the underwater cameras on the sharks' dorsal fins.
Instead, the team concluded that sharks in the small sample may deploy yo-yo diving as a foraging strategy to access food items at different depths.
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Tiger sharks thrive on a variety of foods, including fish, shellfish, crabs, sea birds and mammals. The truth is they're not picky eaters, with one case in which authorities found a chicken coop in a tiger shark's stomach.
Though the observations suggest energy conservation might not give rise to yo-yo diving behavior in tiger sharks, it's important to keep in mind that the experiment sampled a small number of sharks in one area and there might be other factors at play.
It's likely researchers will need to find a stronger link between diving behavior and prey consumption to support their conclusions.
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Image: Wikimedia Commons.
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