The already-depleted population of the popular sport fish white marlin may be in even worse shape than scientists had thought, according to a study published last month in the journal Bulletin of Marine Science.

For years, fishermen have been catching a similar-looking species that researchers now identify as the roundscale spearfish, creating the mistaken impression that white marlin were more plentiful. The roundscale spearfish is almost identical but has rounded scales and slightly different fins.

"This is a case of mistaken identity," said Mahmood Shivji, lead author and director of Guy Harvey Research Institute at Nova Southeastern University.

Environmental advocates have tried to list the white marlin as an endangered species because its population has fallen 88 percent below the level considered healthy, but they have not won federal protection for the species.

Shivji, who conducted a DNA analysis of several species of Atlantic billfish, determined that 16 fish caught by fishermen in the northwest Atlantic were roundscale spearfish, not marlin.

"The question is what proportion of 'white marlin' are actually roundscale spearfish," Shivji said Friday. "That's just a question that needs to be urgently addressed."