While the number of bigeye tuna, a favorite of Japan's sashimi market, has been cut by about 70 percent due to overfishing, other species, such as aku and albacore, have shown minimal drops of about 5 percent, said John Sibert, manager of the University of Hawaii's pelagic fisheries research program and one of the authors of the study.

"The impact varies from species to species," Sibert said Thursday.

He said the study was intended to refute research from 2003, also published in Nature, that said populations of large open-ocean fish in the Pacific, including all types of tuna, had been fished down to 10 percent of their original numbers.