A young great white shark that had been in captivity at Monterey Bay Aquarium died shortly after being released just days ago, the aquarium announced Wednesday.

The 4-foot-10, 52-pound shark was placed back in the Pacific Ocean off Goleta on Oct. 25. A transmitter designed to be released if something happens to the shark popped free Oct. 29 and was recovered the next day, and researchers determined the shark had died.

“This is a very difficult day for all of us, and for everyone who saw and cared about this animal,” said Jon Hoech, the aquarium’s director of husbandry. “Based on the shark’s behavior and condition prior to release, we had every confidence that he’d do well back in the wild. Unfortunately, that’s not how things turned out. We’re surprised and saddened by the outcome.”

It was the sixth great white kept at the aquarium, which has managed to keep sharks in captivity longer than any other institution, ranging from 11 days to more than six months. This shark was released after 55 days, during which more than 250,000 visitors came to see him.

One recent survey showed little more than 200 adult and juvenile sharks off the coast of Central California, though it is not certain how accurate that count is. The Monterey Bay Aquarium said it would review all policies and procedures following the shark’s death.

One other Monterey Bay Aquarium shark is known to have died a few months after release after it was caught in a fishing net off Baja California.

Since 2002, the aquarium has tagged and tracked dozens of great whites as part of Project White Shark, aimed at learning more about the ocean’s top predator. The program is expected to resume next summer, including potentially bringing another great white to Monterey.

The shark was released because it had been navigating the exhibit exceedingly well, movements that could cause abrasions that lead to infections.

Aquarium researchers don’t know why the shark died.

“I don’t think we will ever know,” spokeswoman Karen Jeffries said.

The shark was initially captured in mid-August off Marina del Rey and gained 9 pounds while in captivity.

“While we determined it was best not to keep him on exhibit any longer, we had no reservations about whether the shark would do well in the wild,” said Mike Murray, a staff veterinarian. “That’s why his death is both distressing and puzzling.”

Sharks have been in the news recently, with numerous sightings, including one Wednesday at a Rip Curl surfing competition at San Francisco’s Ocean Beach. A surfer was also attacked last weekend at Marina State Beach, sustaining non-life threatening injuries.

Recently, the state Legislature banned the sale or possession of shark fins, a popular delicacy in a ceremonial Asian soup though the practice of shark finning contributes to global declines in shark populations. The Monterey Bay Aquarium sponsored the bill.

The Aquarium’s shark program is intended to help generate support for great whites, an attempt to reverse a savage image fueled by popular culture, including movies like “Jaws.”

They are the top predator of marine mammals but are listed as endangered despite no accurate count of their population, and dogs kill more people annually than sharks.

“Our animal care staff is unrivaled in its knowledge of young great white sharks,” said Jim Hekkers, the aquarium’s managing director. “I’m proud of the passion and dedication they demonstrate each day. This is a difficult time for all of us.”