Scientists have developed a more accurate way of measuring populations of opihi, a Hawaii delicacy and fixture of first-birthday baby luau and graduation parties in the islands.

Researchers used an Android cellphone app and GPS to help them count each opihi on rocky shorelines within parts of the federally protected Papahanaumokuakea Marine National Monument.

This allowed them to count more opihi more quickly than before.

For example, initial surveys indicated French Frigate Shoals, or Mokupapapa, had between 10,000 and 13,000 opihi. But during this summer’s expedition to the monument, scientists determined the atoll has 3,000 limpets, lead researcher Chris Bird of Texas A&M University, Corpus Christi, said Wednesday.

Scientists aim to assess how opihi populations in the monument vary over time, as well as measure their genetic diversity, Bird said.

The prized limpets are overharvested in the main Hawaiian Islands and are now rarely found on Oahu. A gallon of opihi can go for $150 to $200.

Bird said the team’s research on the genetics of different opihi will allow scientists to understand how human harvesting affects populations and how opihi move around different geographic areas.

It will also enable them to identify what places serve as opihi nurseries and thus are important for the replenishment of opihi populations. This could help regulators protect these zones and lead to the recovery of opihi numbers.

In the remote, pristine environment of the monument, researchers saw thousands of opihi stretching out in front of them, said Hoku Johnson, principal investigator on the research expedition.

At Necker Island, or Mokumanamana, she counted 1,000 within the span of her outstretched arms.

"And I’m 5 feet 6 inches tall," said Johnson, who is also the National Oceanic and Atmospheric Administration’s acting deputy superintendent of policy and programs for the monument.

This is what the main Hawaiian Islands must have looked like 150 to 200 years ago, before overharvesting, she said.

"There’s opihi everywhere," she said. "I’m an Oahu girl, so you don’t see that here."

Johnson hopes that one day in the future, the main Hawaiian Islands will look that way again.

"Opihi will come back if we can figure out a way to manage them appropriately," she said.

The research is part of a broader, multiyear study of rocky shorelines in the Northwestern Hawaiian Islands.