A study of migrating fish in the north Pacific suggests that Japanese and American tuna stocks are the same.
Thousands of salmon, tuna and other fish were monitored with implanted microchips, as part of the Census of Marine Life, which involves thousands of scientists from 73 countries.
According to satellite records of an electronic tracking device, one bluefin tuna swam across the Pacific three times in 600 days.
The fish travelled 40,000 kilometres, equivalent to the distance around the world.
Researchers say the study, which finishes in 2010, will identify Pacific migration routes that that may give clues about how to rebuild fish stocks.