A Prickly shark spent about 15 hours at the Monterey Bay Aquarium, after being captured last night off the Monterey coast.
The aquarium tagged and released it today because it wasn't doing well in captivity.
But marine biologists say it was still an invaluable experience.
"The prickly shark is a deep water shark not even a whole lot is known about its biology so we're learning just observing this animal all the time," said curator Steve Vogel
This is only the second time a Prickly shark has been seen in captivity. The first time was also at the Monterey Aquarium, almost 20 years ago, and it was released after seven days.