The nesting season is over, and Hawaii’s green sea turtles are now returning to the main islands. This year, however, don’t be surprised if you see a number painted on their shells.

It’s no prank.

Scientists are turning to the public for help in an effort to gain a better understanding of where breeding turtles hang out and forage in the main Hawaiian Islands.

The numbers were affixed to the turtle shells this summer by biologists with the National Oceanic and Atmospheric Administration at French Frigate Shoals, a key nesting site for Hawaii’s green sea turtle population.

NOAA’s Marine Turtle Biology and Assessment Program in Honolulu is now hoping you will report any number you see and maybe even take a photograph.

“It’s a unique opportunity for the people here in Hawaii to be connected to our program and help build our database and help build our understanding about the movement of these animals, their distribution and their habitat,” lead scientist T. Todd Jones said Friday at a news conference at NOAA’s Ford Island headquarters.

Every year, green sea turtles make the 1,200-mile round-trip haul from foraging habitats in the main islands to reproduce and nest in the Northwestern Hawaiian Islands and then swim back.

NOAA biologists have made an annual trip to French Frigate Shoals to monitor turtle nesting activity since 1973. This summer they worked to count nests, tag nesting females and count how many hatchlings emerge from their nests.

“We were there 24/7, living there, working there in this remote camp,” field camp leader Marylou Staman said. “There were turtles everywhere. There were birds, sharks, monk seals. To see that much wildlife and to be part of it, that was amazing.”

It was a busy three months. The team saw five times the number of nesting turtles that were observed last year, when there were 87 nests. While it was a banner year, they said, it actually fell short of 2014, when 811 turtles nested on the shoal’s East Island alone. The fluctuation in nesting numbers is typical, they said.

As they have in the past, the field researchers used a small dremel tool to gently etch a number into each turtle and then used nontoxic white spray paint to allow the number to pop out. The method allows the workers to keep track of the animals they already tagged.

The idea of a citizen science project emerged later.

“It was an accident, honestly,” said Irene Kelly, NOAA Fisheries sea turtle recovery coordinator.

The program, she said, received several calls from people who spotted the numbers, and the scientists realized this was an opportunity to engage the wider public in the conservation effort and expand the marine turtle knowledge base at the same time.

Each year, biologists are able to attach a few satellite tags that allow for some high-tech tracking, but that effort is expensive. By comparison, this effort is low budget and has potential to pay big dividends, scientists said.

Nearly four decades ago green sea turtles were rare in the main islands. Today it is common to see them swimming, feeding and basking on beaches throughout Hawaii. State and federal protections paved the way for a comeback, and the population is recovering at a pace of 5 percent a year.

Hatchlings typically emerge from their nest at night and ride the currents of the open ocean, feeding and growing for about five or six years until they’re about 14 inches in length. At this age and size, they return to the islands and settle in the nearshore coral reef habitats.

When they reach sexual maturity between 25 and 35 years of age, the turtles attempt their first reproductive migration, returning to the same beach where they themselves hatched, in order to nest and produce the next generation.

This year 871 turtles — males and nesting females — received a painted number. Turtles that nested on East Island were numbered from 1 to 500; T or G series numbers were given to females that nested on Tern or Gin islands; M series numbers were put on males that made the migration.

The paint is expected to wear off in a few months, officials said, and the etched number will eventually disappear as well.

“We absolutely want the public to report these numbers,” Kelly said. “Once we know where those important habitats are for the turtles, then we can better manage and work with the public to better protect the turtles.”

But she cautioned the public to stay at least 10 feet away to avoid bothering or harassing a turtle.

If you see a numbered turtle, call 888-256-9840. This is also NOAA’s new statewide marine animal reporting hotline, where people can report sightings or emergencies for sea turtles, monk seals, dolphins and whales. The program can also be reached by email at RespectWildlife@noaa.gov.