Spearfishing sportswoman Kimi Werner said that as a youth diving in Maui waters, she’d rarely see a roi fish.

But now, roi have increased in numbers to the point where they seem to be reducing the number of native fish, said Werner, who supports tournaments targeting the killing of the alien species. Roi eat other fish, shrimp and lobsters.

"It’s totally a good idea and a positive thing," said Werner, the 2008 Women’s National Spearfish Champion. "It’s just crazy how quickly they’ve developed."

Werner is among divers who have supported a growing number of annual spearfishing tournaments to kill roi, also known as the peacock grouper, and other alien species such as ta’ape and to’au in Hawaii waters.

The fourth annual "Maui Roi Roundup" involving two-person dive fishing teams takes place Sunday in West Maui.

Brian Yoshikawa, one of the founders of the roundup, said the idea has spread to other dive groups on most Hawaiian Islands.

Yoshikawa, owner of Maui Sporting Goods, said the idea was to create a tournament that would enhance the environment for native fishes.

"Basically, we wanted the divers to be more involved in being stewards of the reef," Yoshikawa said. "If we don’t do it, who will?"

State officials introduced the roi, or Cephalopholis argus, from French Polynesia to Hawaii waters as a food fish in the 1950s.

But in Hawaii most roi now carry the ciguatera toxin, which means they aren’t usually sought as a food source.

According to the Centers for Disease Control, ciguatera fish poisoning is an illness caused by eating fish that contain toxins produced by a marine microalgae called Gambierdiscus toxicus. People who have ciguatera can experience nausea, vomiting and neurologic symptoms such as tingling fingers or toes.

Yoshikawa said the roi caught this year will be given to a farmer to be used as fertilizer.

Darrell Tanaka, another tournament founder and a spear fisherman, said the roi is an opportunistic feeder.

A study done in Hawaii found a 11/2-pound roi eats about 146 reef fish a year.

Tanaka said that since the tournament began, spearfishers have removed more than 2,000 roi from West Maui reefs. He said 800 were caught in one tournament on Molokai.

Tanaka said the tournament has been effective in reducing the roi population, and he’s noticed fewer of the fish since the tournament began in 2008.

Oahu resident Kris Tyler said interest is growing in his "Roi Reckoning" spearfishing tournament.

The last event at Ko Olina attracted 30 two-person teams.

"Each year the tournament’s gotten bigger," said Tyler, owner of Westside Dive & Tackle.

University of Hawaii researcher Alan Friedlander said he’s noticed large roi populations in South Maui and Kona.

Friedlander, an associate professor at the university’s cooperative fisheries research unit, said he’s not about to tell people to stop killing roi.

But Friedlander said he has conducted research on Hawaii island to determine whether native species return once the roi population is reduced.

"We don’t have the answer yet," Friedlander said. "Hopefully within the next year we should have some results."

For information, contact Tanaka at 575-2557 or roiroundup@gmail.com.