The peacock grouper – a fish better known in Hawaiʻi by its Tahitian name roi – has become a dominant predator on local reefs. It devours native fish and competes for their food sources.
One young Hawaiian scientist is leaning on the centuries-old practice of kilo — or observation — to reduce the impact of the invasive roi.
Fishing communities like Miloliʻi on Hawaiʻi Island have been sounding the alarm on roi for years. These dark brown fish have small iridescent blue spots and purple fins.
They can grow up to two feet in length. One of the big drivers of its dominance on reefs is not having any natural predators here.
Invasive roi in Miloliʻi
Heʻeia native and environmental policy student Kainalu Keliʻikuli-Grace spent his summer creating a baseline study on roi in Miloliʻi in South Kona.
“When I jumped in over there, it was like a roi haven,” Keliʻikuli-Grace said. “It was loaded.”
He couldn't pinpoint roi populations with certainty, but his rough estimate was at least 15,000 roi along the 18-mile coastline of Miloliʻi. Keliʻikuli-Grace gained most of his insight on roi from kilo, or observation.
He observed roi are easier to catch at dawn and dusk – that's when they hunt. He also estimated harem sizes to be about one male roi per 20 females. He noticed roi prefer the dark, shallow areas of the reef with lots of coral cover and crevices.
“They just love dark spaces and they're big fish but they squeeze into these tiny little spots,” Keliʻikuli-Grace said.
He also monitored the roi behavior, and noted a particular interaction between roi and another dominant reef predator, the puhi, or eel.
“Every time you follow the puhi, you're gonna find roi. When the puhi goes into like these small crevices and stuff that the roi can’t necessarily fit into, all the baby fish, the puaiʻa, they fly out scared of the puhi, and the roi is just right there to come snatch them up,” Keliʻikuli-Grace said. “I don't know if this is a symbiotic relationship. It's more just kinda like, ho, these roi they pilau taking advantage of the puhi over here.”
Impact to Miloliʻi reef fish
In Miloliʻi, about 18 miles of the coastline were designated a community-based subsistence fishing area in 2022. So there are fish that the community is trying to protect in order to boost populations like kole, uhu, and especially pākuʻikuʻi.
Keliʻikuli-Grace examined the stomach contents of about 50 roi for insight into dietary trends — a tricky undertaking.
“Because when you dispatch the roi they tend to palu up their stomach. So I'm over there grabbing whatever's in the water, sticking it into my wetsuit, probably one manō buffet,” Kainalu-Grace said. “But what I did get is ʻoama, kole, manini, and especially reds like ʻūʻū, ʻalaʻihi, āweoweo, they really love their reds. Two out of those three are protected species in Miloliʻi.”
Keliʻikuli-Grace noticed some of the bigger roi he caught had consumed sizeable fish that he would have caught himself as a fisherman. He said the smaller roi go for the invertebrates like baby lobster, baby shrimp, wana, tako — sources of food for other reef fish.
“So it's not only eating this native fish but it's competing for food sources also,” Keliʻikuli-Grace told HPR.
Roi introduced to Hawaiʻi in the 1950s
Keliʻikuli-Grace grew up in the ocean — surfing, fishing, and diving on the east side of O’ahu. Growing up, he said, he's noticed more and more roi on the reefs.
Roi were brought to Hawaiʻi from Moʻorea in the 1950s. A little over 2,300 roi were introduced to Hawaiʻi during the territory to help boost our fishing stocks. Roi was one of about 20 species of snappers and groupers introduced over the period of about five years starting in 1956.
Other introduced species from this time that established populations in Hawaiʻi are also known by their Tahitian names taʻape and toʻau. Both came from Moʻorea as well.
By the 1980s, the roi population had skyrocketed — increasing 15-fold across the islands to about 35,000. But ever since roi was linked to ciguatera food poisoning — a type of food poisoning — roi has been off the menu for most households in Hawaiʻi.
Ciguatera fish poisoning
Ciguatera is a naturally occurring toxin. Ciguatera fish poisoning can cause nausea, vomiting, and other symptoms. The state Health Department reported 123 ciguatera fish poisoning cases in Hawaiʻi over the last 10 years, including nine so far this year.
More study is needed on the prevalence of ciguatera in Hawaiʻi's roi populations. A 2009 UH study on ciguatera in roi found an 18% positivity rate, but these rates vary throughout the Hawaiian Islands.
There’s no particular coastline that produces more ciguatoxic roi. And ciguatoxin levels vary throughout the Pacific. Places like Tahiti have high instances of ciguatera, while fisheries in Palau have little to none.
The DOH Disease Investigation Branch said ciguatoxins cannot be eliminated or reduced by heat, cooking, drying, salting or freezing the fish. The highest concentrations of toxins can be found in the liver, intestines, eggs, or head of the fish.
The CDC also advises that it can be difficult to tell if fish is contaminated as the toxins that cause ciguatera do not change the appearance, taste, or smell of the fish.
Ciguatera tests and screening methods
The state used to provide free ciguatera tests to the fishing community, but those tests turned out to be inaccurate. Tests appeared very sensitive to residual amounts of ciguatoxins and were producing a high number of false positives.
DOH said it's working with the Food and Drug Administration to test ciguatera in fish. But the only other option for fishing communities is lab tests, which can cost $300 to $400, Keliʻikuli-Grace said.
But Hawaiʻi isn't the only place where communities have had to deal with ciguatera in roi. Keliʻikuli-Grace found that people in Fiji love eating roi, but also deal with ciguatera.
“What they'll do is use like the village cats in Fiji. I was like ‘Ho, I’m in Miloliʻi, I get cats, I get mongoose, I get eels. We go try,'" said Keliʻikuli-Grace. "One of the village cats, ʻEhu, she was the best at that. She went like 20 for 25 on guessing. Whichever ones had the clotted blood, she’d walk right past.”
He tested this and a few other methods used in Fiji, including using puhi instead of cats and examining the tail end of roi. White meat is safe. Dark purple, clumpy meat means ciguatera.
Puaʻala Pascual, Ahupuaʻa Accelerator Coordinator at the Hawaiʻi Conservation Alliance, said Keliʻikuli-Grace’s initial observations and screening methods were empowering.
“You’d need a slightly more rigorous lab test to be able to confirm what is or what is not testing for cig(uatera),” said Pascual. “But that initial observational knowledge, cig screening methods...that center Indigenous and local lawaiʻa knowledge was the most meaningful to me because I’m currently working with some community partners who are heavily involved in lab testing.”
Roi roundups
The most effective tool in reducing roi’s impact on local fisheries has been the roi roundups — fishing events that aim to reduce the biomass of roi in a particular fishing ground by boat, pole, or spear.
Much of what we know locally about roi — diet, habitat, breeding, etc. — comes from these roi roundup events. Pascual, who works with some of these communities on this issue, said Keliʻikuli-Grace’s research could have an impact on these events.
“So being able to add on some kind of testing component or just creating more space for lawaiʻa dialogue around those events to see what observations or behavior are our lawaiʻa seeing,” Pascual said. “What kinds of things have they been taught from small kid time from their ʻohana or others about when or when not can you consume a particular species that may be often associated with ciguatera.”
Keliʻikuli-Grace’s initial kilo on roi habitat, diet, behavior, and breeding trends in Miloliʻi helped him come up with ways to improve Miloliʻi’s next roundup.
“We’ll do it on a poepoe moon phase because that’s what I estimate their breeding season is when the moon phase is the largest. And then I noticed in Miloliʻi, only the males had the orange tips on top of their pectorals. So urging people to go after these orange big guys because that’s gonna put so much more of a dent on populations.”
Keliʻikuli-Grace is currently finishing up his senior year at Linfield University, where he is majoring in environmental policy with a minor in environmental economics.
He took part in the kilo-based research project in Miloliʻi as part of his summer internship with the University of Hawaiʻi PIPES Internship Program. He worked in collaboration with the community organization Kalanihale in Miloliʻi to develop a better understanding of how roi impacts the CBSFA. His study was titled, "Oi! We Get Too Much Roi."
“Now, it’s like every time I hop into the water I’m searching for roi,” said Keliʻikuli-Grace. “It's like I don't even care about this ‘ulua swimming next to me. Where's the roi at?”
