Roi, the misunderstood fish
Research reveals more about disliked, introduced species
Over the years, roi have been labeled as a culprit for the declining fish populations and reef health, but marine specialists say these fish may not be as bad as they seem.
Data show that nearshore fisheries were on a slow downturn many decades before roi were introduced to Hawaii, they said Wednesday.
“We got historical problems with overfishing in Hawaii, so we have to be very careful at what those root causes are,” said Alan Friedlander, chief scientist of National Georgraphic’s Pristine Seas project and director of the Fisheries Ecology Research Lab at the University of Hawaii. “A lot of people like to point at different things — it’s roi, ta’ape, it’s pollution, habitat loss.
“A lot of those are true, but not one thing is causing the decline in nearshore fish.”
During the Maui Nui Marine Resource Council’s monthly “Know Your Ocean” speaker series, which is being held via Zoom due to the COVID-19 pandemic, marine specialists said there has been about a 90 percent drop in catch rates of the “resource fish that we know and love” over the past 100 years.
Concerns have been raised over roi’s diet of smaller native fish and the toxins carried in its flesh that can make people sick. As a result, communities throughout Hawaii have organized roundups and spearfishing events that target the introduced roi.
“Fishery resources have been on the decline for quite awhile, even as early as the 1900s; we’ve got records showing that nearshore fish have been overfished, over-exploited, and that continues on through the years,” Friedlander said. “We’re not starting from a recent problem, we’re starting from a fairly significant historical problem, and some of that is evident in the catch data that we have dating back from the early 1900s.”
Localized overfishing is referenced all the way back to 1902 in Honolulu, and again in 1923 in the Ka Nupepe Kuokoa newspaper. Territorial Fish and Game Commissioner Hercules Kelly also noted in 1925 that Hawaii’s waters showed signs of wasteful fishing methods and techniques and overfishing.
Roi, also called peacock groupers for their colorful spots and stripes, are moderate-sized predatory fish that can be found in habitats ranging from French Polynesia to the coast of West Africa.
They have long lives and are slow growing, with the oldest roi around 25 years old. Roi are found in depths from shallow tide pools to 130 feet deep but are more commonly found where there is more fish, whether in open ocean or marine protected areas.
They also prefer “complex” habitats with coral cover for places to hide and to ambush prey.
During a study on Hawaii island, the dominant fish species found in the stomachs of roi were squirrelfish, about 25 percent, followed by surgeonfish, 13 percent, and bigeye, 8 percent, Friedlander said.
Some believe that roi may also be preying on yellow tang, but data from the Department of Land and Natural Resources Division of Aquatic Resources showed no significant correlation between yellow tang and roi numbers through the 1990s and 2000s near Hawaii island.
“They eat a mix of different species, and nothing in particular comes out as being the dominant prey items for them,” he said.
The marine circle of life between the predatory fish and the prey is essential for a healthy ecosystem, said Russell Sparks, aquatic biologist for the DLNR Division of Aquatic Resources Maui Division.
“Predators are playing a really important role in kind of calling that out, eating the sicker ones, the ones that are not quite as smart, and driving some of those adaptive changes over time to make all these fish more productive,” Sparks said. “And to improve the whole ecosystem, predation is really, really important on coral reefs.”
Roi only eat about 2.5 times their body mass over a year, while other predator fish, like omilu, eat up to 10 times their body mass, Sparks said.
“That’s substantial in driving the ecosystem and predation pressure, so without having more things like roi around could be important,” he said. “And I say ‘could’ because we don’t know all of these little intricacies for certainty.”
Sparks said that the department does not discourage roi hunts, but marine reserves will remain protected for research purposes.
Roi were introduced to Hawaii in the 1950s with the idea that they could provide food options for the community. However, roi became known to cause ciguatoxin, a type of food poisoning, and fishermen avoided eating them.
“There are definitely people that go out there and eat roi,” Friedlander said. “People feel that there are certain places that have lower incidences of ciguatera and others just take the risk.”
He added that of the 291 roi that were examined on Oahu and Hawaii island during a study, about 46 percent of them tested negative for ciguatera, about 36 percent were “marginal,” and only 18 percent were positive.
“So they are not all ciguatoxic,” Friedlander said. “It’s not directly related to the size of the animal as well. It’s kind of an enigma to some degree.”
Ciguatera is a naturally occurring bacteria and is more or less prevalent in certain areas. French Polynesia is notable for its ciguatera poisoning with roi as a culprit, whereas inhabitants of other places readily consume roi because there are no traces of the bacteria.
Additionally, ciguatera can be “stirred up” by increasing human populations, shoreline developments and disruption of habits, events that began to increase in the 1950s and ’60s in Hawaii.
“In general, things tend to be more ciguatoxic now than they were, and the work that has been done on roi showed the highest concentrations were typically around Oahu and some parts of the Big Island that had more human disturbance,” he said.
With a low mortality rate of about 14 percent a year, roi began to really populate Hawaii waters in the 1990s and were considered an aggressive and invasive species that consumed smaller reef fish.
As a result, spearfishing events and roi roundups started on Maui and other places to remove them from local reefs.
To discover the truth about roi, Friedlander said that they partnered with The Nature Conservancy and the Division of Aquatic Resources on Hawaii island at Puako to see if roi could be removed from a site, which would be then tracked.
Researchers studied the overall fish community with the absence of roi by first studying immigration rates into the area from November 2010 to May 2015. Roi then were removed and tagged about 27 yards from the site.
New roi moved into the area about every six weeks, and one diver entered the area every eight to 12 weeks to keep the reef clear of the immigrant roi, he said.
“The overall big picture is, after five years, there is no effect on juvenile fish — these are fish smaller than 15 centimeters (6 inches),” he said. “After roi were removed, for the first year and a half, we see a slight increase in the amount of small fish in the treatment site that didn’t have roi in them, but you lose that after that period.”
After four years, there were no significant differences between the treatment site where roi were actively removed and the control site.
“That’s a big take home from that study,” he said. “They had a relatively small impact as a reef predator on the nearshore reef community.”
But that’s not to say that the roi roundups and fishing tournaments don’t provide valuable opportunities for scientists and fishermen to collaborate, especially in areas where roi is perceived to be a problem. In fact, Friedlander said “it shares knowledge, builds community awareness” and discovers useful information about roi’s diet, reproduction, life history, aging and growth patterns.
“It’s been collaborative work with the community, and with resource managers and fishers and scientists working on trying to understand roi better,” he added. “A lot of the data we’ve collected and shown so far have been a result of these collaborations relative to these roi roundups.”
Future removal or test projects may require more technical surveys and transects with divers to record the number of roi. Costs for these surveys can run $2,300 for two trained scuba spearfishers, one trained boat captain, and boat access to the fishing area. Shoreline surveys can average about $1,000 for two trained spearfishers.
Volunteers can help to reduce the costs of these surveys and are still encouraged to get involved with data collection and roundups to help learn more about roi.
“Oftentimes people are reaching for something that they can help with, you know, it’s so overwhelming to see fish populations declining and habitats declining, and you want to do something to contribute,” Sparks said.
* Dakota Grossman can be reached at firstname.lastname@example.org.