Look-alike fish may throw off white marlin count

They are sleek, elusive predators, slipping through the deep violet of the ocean depths.

The challenge of catching white marlin has made them a prime target in fishing tournaments, with the winning catch at last summer’s White Marlin Open in Ocean City, Md., reaping $903,442.

But it turns out many fish identified as white marlin were actually a recently discovered look-alike called the roundscale spearfish.

In fact, more than a quarter of the fish caught and identified as white marlin were roundscale spearfish, says a new study by scientists at the federal government, Nova Southeastern University in Fort Lauderdale, Fla., and other institutions. Their findings could call into question the government’s decision to keep the white marlin off the endangered species list.

“South Florida used to be a destination for big white marlin,” said Bouncer Smith, a Miami Beach charter captain who has caught just two in the last 10 years. “They’ve been very rare here for years. Seeing one is a rare treat now.”

The main reason for the decline: White marlin are accidentally caught on commercial longlines set to hook tuna and swordfish.

Two years ago, the Bush administration rejected a petition from the Center for Biological Diversity to put the white marlin on the endangered species list, saying its numbers were starting to rebound after a series of measures intended to protect them from accidental catch. The administration also removed it from the list of species of concern.

But this study, reported in the journal Endangered Species Research, suggests the government relied on data that inadvertently inflated the abundance of the species.

The scientists analyzed tissue samples from white marlin caught accidentally by fishing boats and in tournaments. They found that 27% were actually roundscale spearfish. In other words, there may be a lot fewer white marlin out there than originally thought.

Mahmood Shivji, professor at Nova Southeastern University and director of its Guy Harvey Research Institute, who has made a specialty of marine genetics, said the study suggested the government needed to do a major reassessment of the species’ status.

“This is a high enough proportion to muck up previous population assessments of white marlin,” Shivji said. “In other words, previous data on white marlin is contaminated by another species, resulting in all past stock assessments of the white marlin -- on which U.S. and international management policy has been based -- uncertain.”

Any move to place the white marlin on the endangered species list would face opposition from members of the recreational fishing community, who oppose blanket protections that could eliminate any fishing, even catch-and-release.

David Bernhart, southeast chief of the National Marine Fisheries Service Protected Resources Division, said it’s unclear whether any dire conclusions can be drawn from this study.

The latest government review found that the stock of white marlin was growing, he said. Even if many of the fish counted were the other species, so long as the assessments were proportional, nothing would alter the fact that the stock is growing.

“The simplest assumption right now is that everything is proportional,” he said.

dfleshler@sunsentinel.com