A study led by a Stanford University researcher found the number of the turtles has increased since 1978 when the species was listed under the U.S. Endangered Species Act, the figures still fall short of historic levels.
"It's critical to compare the animal's population level to its historic abundance, not just to recent levels," John N. Kittinger at Stanford's Center for Ocean Solutions said.
The researchers compared contemporary and historical nesting records of Hawaiian green sea turtles from fishery logs, archaeological sites, Hawaiian-language newspapers and first-hand historical accounts.
Analysis of the records indicated 80 percent of major historic green sea turtle nesting sites have disappeared and many others have shrunk greatly in size, the researchers said.
"Hawaiians were able to sustainably coexist with nesting green sea turtles as recently as the early 20th century, when nesting sites could still be found on the main Hawaiian Islands," Kittinger said.
The green sea turtle is an important cultural symbol in Hawaii.
"After traditional harvesting restrictions gave way, we see evidence for population depletion" Kittinger said. "This needs to be considered for sustainable management of the species moving forward, including a potential harvesting program should the species be delisted."