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Shucking the Limitations of Hawai‘i's Aquaculture Industry with Oysters

October 19, 2015

Kualoa Ranch's Moli`i fishpond is the first farm to sell certified grown-to-maturity oysters in Hawai`i in nearly three decades.

Oyster baskets float in the Moli'i fishpond with the a lush green mountainside in the background.

It's a slightly overcast Monday afternoon in September, and we are slowly riding along in a 25-foot sea-foam-green boat. Its motor is barely audible over the breeze as it carries us across a portion of the 125-acre Moli'i fishpond at Kualoa Ranch on the windward (eastern) side of O'ahu.


A few minutes later, we reach our destination some 150 yards from the dock.

"I'm returning these oysters," Ku'uipo McCarty announces as she prepares to lower an approximately 4-foot tall wire cylinder into the brackish pond. The cylinder houses about 150 market-sized oysters, which have been to retail but weren't sold. "We call them recycles, or resuscitations, or reincarnations, because they are still alive but they have gaped a little bit and have been in the refrigerator for five days."

After spending a month in the fishpond, recuperating and hanging out with tens of thousands of other oysters, the recycles will get a second chance to complete their life cycle – in the guts of hungry Hawai'i residents and visitors.

Here at the Moli'i fishpond, the first farm to sell certified grown-to-maturity oysters in Hawai'i in nearly three decades, sustainability and conservation are ideals held dear. For instance, oysters that perish before making it to the market still serve an important role as pothole fillers.

"We made 'oyster island' right over there," says McCarty's assistant Moani Heimuli. "Oyster island and oyster lane."


Ku‘uipo McCarty (front) and her assistant Moani Heimuli (back) offload several oyster-filled baskets from their boat. After being washed with freshwater, these oysters will dry out over night – a treatment that helps kill a parasitic worm that bores into the oysters' shells.

"It's reclaimed land," adds McCarty, who's in charge of the day-to-day operations of Kualoa Ranch's oyster farm. Even McCarty herself, who doesn't have a background in marine science but has been with the ranch for 27 years, is a kind of testament to these ideals.

From Captain to Oyster Farm Manager

A Hawai'i resident all her life, McCarty, a seemingly inexhaustible woman with an equally boundless sense of humor, grew up in the ahupua'a (division of land stretching from mountaintop to ocean) of Hakipu'u, which encompasses Kualoa Ranch and the Moli'i fishpond. "When I was two years old, I grew up looking at the cowboys on the ranch and wishing I could be a cowgirl," McCarty recalls.

Fortunately for her, McCarty's wish eventually came true.

McCarty began her journey with Kualoa Ranch – which would culminate with her running the oyster farm – in 1988 as a Hobie Cat captain in the ranch's tourism department. She then moved on to develop and run the ranch's therapeutic horsemanship program, utilizing her associate's degree in occupational therapy from the University of Hawai'i. In this position, she served the disabled community of O'ahu for 20 years, while simultaneously working for the ranch's education department for about 18 years, she says.

In the mid-2000s, Kualoa Ranch owner John Morgan approached Bruce Anderson, former Hawai'i state health director and current administrator of the Department of Land and Natural Resources Division of Aquatic Resources, to help revitalize the Moli'i fishpond and control the excessive growth of invasive algae, which would otherwise harm the pond's harvestable herbivorous fish. After a failed attempt at controlling the algae with more herbivores – the pond's carnivorous barracuda and ulua (giant trevally) ate them too quickly for the fish to have any real effect on the algae – Anderson began experimenting with raising oysters.

Given McCarty's long personal history in the region and work history with the ranch, Morgan asked her to help care for the pond and assist with the shellfish program. McCarty agreed, and volunteered her time to help Anderson and learn everything she could from him about oyster farming.

"Our process started in 2008, beginning with doing some research and development on whether the oysters did grow in the fishpond, how quickly they grew, and what type of culture system would be best for Moli'i pond," McCarty says. "We grew out 35,000 of them, and we were very successful." 


Created by the oyster farms "founding father" Bruce Anderson, this oyster basket contains a PVC tube that's periodically rolled to prevent the oysters from sticking to each other and to remove feces.

Busy with other duties, Anderson, whom McCarty fondly refers to as the oyster farm's "founding father," eventually handed over the project to her. And for a time, McCarty handled the oysters on her own, before getting two assistants – Heimuli and Ikaika Velez.

"I've worked hard for 27 years to be given the opportunity to do it," McCarty says. "It's just by working for a private company that acknowledges loyalty and hard work and interests, and facilitates the growth of their employees."

"She's really a go-getter," says Alan Everson, NOAA Fisheries' aquaculture coordinator for the Pacific Islands Region. "She's the reason it can happen, it's because of her energy. If it were another person, they probably would have given up."

But just what does it take to raise oysters in a loko i'a, or Hawaiian fishpond?

From Spat to Market-Size

The Moli'i fishpond has been in production since ancient Hawaiians built it 800 years ago, McCarty says, adding that it doesn't need restoration like numerous other fishponds in Hawai'i.

Like other loko i'a, Moli'i fishpond contains brackish water – a mixture of seawater and freshwater from a clean watershed. Separating the ocean from the pond is a permeable, mortar-free wall of hand-laid rocks that were passed hand-to-hand.

The fishpond was designed to be sustainable and self-recruiting, able to draw in and trap herbivorous fish with grated sluice gates. Attracted to algae-filled water, baby fish from the ocean would swim into the pond, and then grow up and become too large to get back out through the gate. This system, which keeps predatory fish populations to a minimum, allowed ancient Hawaiians to maintain large stocks of herbivorous fish.

However, carnivorous fish that people introduced to the fishpond in modern times threw off Moli'i's delicate ecological balance, allowing algae to bloom. But this bountiful vegetative food source, coupled with Hawai'i's naturally warm temperatures, also made the fishpond an ideal home for oysters.

The oyster-growing process begins with 6-millimeter oyster spat (larvae), which Kualoa Ranch gets from a hatchery on the Big Island several times a year in batches of 50,000 to 75,000. McCarty and her assistants transfer the oysters into a 5 mm mesh-lined wire cylinder that holds a PVC tube – an apparatus that Anderson built.

There are several benefits to this design, McCarty says. For one thing, the PVC tube keeps the cylinder afloat, decreasing the predation on the oysters while discouraging disease by keeping the bivalves out of the mud. The system also decreases labor costs by making it easier to clean and roll the oysters, compared with traditional methods of growing oysters in bags.

The team places the oysters, in their cylinder baskets, out into the pond in an area specified by the Department of Health (this makes it easier for the department to conduct their safety tests, McCarty says). Every day, they roll the PVC pipe in the water, preventing the spat from sticking to each other or the cylinder while also helping to remove feces. They also give the oysters a thirty-minute freshwater bath once a week.

Once the oysters get big enough, McCarty and her staff move them into the next cylinder, which has a half-inch mesh liner. Different for each oyster, this growth period can take anywhere from three weeks to three months, McCarty says.

The oysters will stay in this cylinder for another two to three months, and continue to get rolled once a week. The team also removes the baskets from the pond, gives them a freshwater bath, and allows them to dry out overnight each week.

This weekly drying treatment – devised through research and consultation with scientists and experts, including Everson – helps kill Polydora, a parasitic worm that bores through the oysters' shell. While the worms don't kill the oysters, they do create blisters on the inside of the shells. "And if you didn't know how to shuck and you accidentally hit it, it would sour the oyster," McCarty explains.

Eventually, the oysters will move on to a liner-free basket, which has wire with an inch-sized spacing, until they're ready for harvest.

For the harvest, the team takes the oysters out of their basket and lines them up neatly on a table, allowing them to see if any of the bivalves have died and should be added to oyster island and oyster lane. Those that survived are placed in a 200-gallon depuration tank, which recirculates artificial seawater and sanitizes it with UV light, for 48 hours. This important step empties out the oysters' guts, making them safer for consumption by preventing the transmission of any feces-borne illnesses that have travelled down from the watershed and into the oysters. The oysters are then sent off to retail.

"She's been doing an excellent job with a limited amount of resources," comments Everson. "You can see how labor intensive [the process] is."

"Because of the magic of the Moli'i fishpond – the prolific amount of phytoplankton and our warm temperatures – we can get a harvestable-sized oyster from a 6-mm spat to a lovely half-shell size in six to seven months," McCarty says. This is just a fraction of the time it takes to grow oysters on the mainland.

All of Moli'i fishpond's bivalves are sterile Pacific oysters (Crassostrea gigas). "We grow a specific variety called a triploid," says McCarty, who can seamlessly switch from pidgin (Hawaiian creole) to academic speech. "It is bred in hatcheries by crossing a diploid, which is a regular breeding oyster that has two sets of chromosomes, with a tetraploid, which has four sets of chromosomes and naturally occurs in nature but is rare."

Raising only sterile oysters keeps the population in check, allowing the bivalves to clean up the fishpond but not take all the food (algae) away from Moli'i's herbivorous fish, which McCarty, Heimuli, and Velez also harvest for the ranch. In this way, the team can keep a sustainable supply of both oysters and fish.

Breeding the oysters is "very similar to taking a donkey and a horse and making a mule," McCarty says. "They are hardworking but they're sterile."

From Ecology to Economy

With only a small patch of algae – no bigger than the oyster-harvesting boat – left on the surface of Moli'i fishpond, the oysters' ecological benefits are obvious. The bivalves effectively take up microalgae, preventing them from forming dense mats on the water surface. In years past, McCarty notes, the algae would cover an average of 15 to 35 percent of the pond, and at worst the entire fishpond.


The oysters at the Moli‘i fishpond help control the growth of algae, which can sometimes cover the whole pond. Thanks to the bivalves, this small algae patch is all that's left.

Though the oysters were primarily envisioned as ecological tools, Kualoa Ranch recognized the mollusks' economic benefits early on. In order to sell raw oysters to the public, however, the fishpond would need to meet certain safety regulations put in place by the U.S. Food and Drug Administration.

Interestingly, when Kualoa Ranch first began raising oysters, the Hawai'i State Department of Health was not up to the task of certifying farms for shellfish production. The department's laboratory and food safety program underwent an intense federal recertification and training process.

In early 2014, after 18 months of water quality tests, Moli'i fishpond became one the first operations to receive state certification to market shellfish in some 27 years. "We follow Department of Health guidelines and we will be tested into perpetuity," McCarty says.

After receiving state certification, McCarty began selling Kualoa Ranch's oysters at the ranch's Visitor Center, and then to individual restaurants soon after. She estimates that she now sells about 1,500 oysters a week – this money goes to the ranch, which solely funds the oyster farm project at Moli'i fishpond. By comparison, Hawai'i imports an estimated 400,000 oysters a month, she says.

Oyster farming could become a multimillion-dollar industry in the near future if other fishponds across the Hawaiian Islands take after Kualoa Ranch's lead. "We're hoping that slowly more people will come on board and start to," Everson says. "There's a chance to expand the aquaculture industry."


As part of the harvesting process, Ku‘uipo McCarty and her assistants neatly lay out the oysters on a tray, allowing them to easily pick out those that have perished.

Other fishponds, including He'eia fishpond on O'ahu, are looking into raising and selling triploid oysters, but none have been certified yet. Moli'i is, in a sense, lucky in that it has a very clean watershed, which keeps the amount of fecal contamination that gets into the oysters relatively low, Everson says. Longer depuration times or more sophisticated depuration techniques are likely required for various other fishponds to obtain certification, he says.

Importantly, depuration not only makes consumption safer, but also improves the oysters' taste. Everson rates the oysters as some of the best he's ever had, a sentiment shared by both long-time oyster lovers and the newly converted.

"Our biggest joy is to provide a quality product, home-grown in Hawai'i, to our local consumer," McCarty says. "And many of the people have said that it is a sin to cook or even put anything on our oysters because they're that delicious."

Last updated by Pacific Islands Regional Office on April 28, 2022