A new study by scientists from Hawaii and California suggests that the world’s diminishing shark populations may be more precarious and vulnerable than previously believed.

The eight-year shark tagging project — the largest such survey ever accomplished — counted far fewer sharks than previously estimated at pristine Palmyra Atoll, 1,000 miles south of Hawaii.

The authors of the study, published in the journal Scientific Reports, recommend lowering shark catch quotas to reflect the new “baseline” data and prevent over-exploitation of the key ocean predators.

“Shark populations have been decimated in many areas around the globe,” Darcy Bradley, the study’s lead author and researcher at the University of California, Santa Barbara, said Friday.

Led by the Nature Conservancy and UCSB, a team of scientists conducted shark tagging between 2006 and 2014 at Palmyra Atoll, which is both a Nature Conservancy preserve and U.S. Fish and Wildlife Service national wildlife refuge which has been off-limits to fishing since 2001.

Focusing on Palmyra’s top ocean predator, the gray reef shark, scientists estimated a population between 6,000 and 8,000, which works out to a density of just over 21 sharks per square kilometer. Previous estimates ranged from 200 to 1,000 sharks per square kilometer.

Despite the substantially lower numbers, the study found that the shark population at Palmyra is healthy, thriving and stable, a fact that indicates a healthy shark population can be much smaller than previously thought.

The study, according to the authors, helps reset the base line for what a shark population looks like when it is free of the pressures of fishing and other human-related threats.

“You don’t have to have a million sharks everywhere to have a healthy reef,” said Eric Conklin, director of marine science for the Nature Conservancy’s Hawaii and Palmyra programs.

The good news, Conklin said, is that restoring threatened populations might not take a huge effort.

“It’s not the impossible goal that we once thought,” Bradley said.

The study suggests that current shark recovery targets are unrealistically high and need to be adjusted accordingly.

However, the downside is that smaller populations are much more vulnerable, Bradley said.

Three years ago a study spearheaded by the Shark Specialist Group of the International Union for Conservation of Nature found that 25 percent of the world’s sharks are closing in on extinction.

The global analysis of the conservation status of 1,041 shark, ray and related species found that at least 1 in every 4 species of sharks might soon no longer exist in the world’s oceans. The study said overfishing was largely to blame for the declining numbers.

Scientists in the Palmyra study said previous shark population estimates were calculated using less sophisticated visual methods.

During their study the Palmyra researchers tagged 1,300 reef sharks and fitted them with numbered ID tags. Of the animals tagged, 350 were recaptured.

Researchers recorded information on the sex and size of each shark and the location of its capture, and fitted some of the sharks with acoustic telemetry tags that broadcast the animal’s location to a vast system of receivers set up across the atoll.

Armed with eight years of data, the scientists used an algorithm to estimate the population size.

Despite the lower estimates of shark abundance, Conklin said the density of the animals is still quite impressive, especially compared with the main Hawaiian Islands.

“It’s rare to jump in the water at Palmyra and not see several sharks,” he said. “In Hawaii it’s a very rare thing to see any sharks.”

The scientists said the findings indicate that island states and other ocean regions may be able to restore their own shark populations by setting up marine managed areas to protect sharks throughout their home range.

That includes Hawaii and its tourism industry, which usually has an aversion to sharks for fear of attacks.

But Bradley said shark attacks are actually quite rare in a larger context, while shark tourism can generate big bucks. The Bahamas, for example, takes in $100 million annually, representing 1 percent of the country’s GDP, she said.

Another key finding in the report is that reef sharks at Palmyra spend most of their time within the atoll without traveling great distances, as preliminary results had suggested.

Scientists said Palmyra and its 15,000 acres of surrounding coral reefs are one of the few places left where sharks and other large apex predators dominate the marine ecosystem.

“It’s a beautiful, amazing, wonderful, pristine corner of the world,” Conklin said.

It is off-limits to commercial fishing and has never had a permanent human settlement, except by the U.S. military during World War II.

Other researchers in the study included Kydd Pollock of The Nature Conservancy; Douglas McCauley, Bruce Kendall, Steven Gaines and Jennifer Caselle from UCSB; former University of Hawaii researcher Yannis Papastamatiou of Florida International University; and Amanda Pollock of the U.S. Fish and Wildlife Service.