Good Data, Unexpected Solutions

When a seafood novice arrives at Tomales Bay, one of California’s foremost oyster-farming hotspots, he or she might look at the piles of iced oysters ready for sale and see, well, oysters.

Just anonymous hunks of shell, that is — gnarly on the exterior, luminescent inside, holding a delicious slurp of briny meat.

A more serious diner may pay attention to the nuances of different species grown here: Pacific or Eastern or Kumamoto, and so on. Even more refined palates might distinguish the “merroir” produced by the water conditions at specific farms. But if you really know your oysters? That’s when you start thinking about genetics. 

Hog Island Oyster Co., for example, one of the farms in Tomales, conducts studies on the oyster “seed” that’s grown at the company’s in-house nursery. Lately, they’ve been examining oyster “lineages” — populations derived from specific seedstock — and what happens when they cross them. "We're asking how different genetic lineages perform differently across estuaries on the West Coast," says Gary Fleener, Hog Island's director for science, education and policy.

A few years ago, the company approached California Sea Grant asking for help with data analysis. And as it turns out, good data on oyster genetics can help the industry in surprising ways.

From Miyagi to Midori

Five different oyster species are commonly raised on U.S. farms, but in California, one is far and away the most popular: the Pacific oyster, Crassostrea gigas. Native to Asia, the species was introduced in British Columbia in the early twentieth century. These first oysters proved amenable to varied habitats and culture methods, so farmers brought them south, across the border, until they became the local standard. Since the Asian source for these oysters was in Japan’s Miyagi Prefecture, and since almost all of California’s oysters are descended from that first population, the local oysters are known as the “Miyagi” lineage.

But oyster farmers have not been letting their oysters breed willy-nilly. Instead, for thirty years, Oregon State University’s Molluscan Broodstock Program has been carefully selecting descendants of those original Miyagi oysters, specifically targeting growth rates and survivorship. “It’s a free service they provide, so that other hatcheries can produce good oysters at commercial scale,” says Kevin Marquez Johnson, the California Sea Grant Aquaculture extension specialist at California Polytechnic State University-San Luis Obispo.

In the early 2000s, a group of researchers traveled to Japan, aiming to collect specimens of a different oyster species — Kumamoto oysters, Crassostrea sikamea, the second-most-popular in California, which are known for their small but deep cup and fruity flavor. The idea was to add diversity to U.S. stocks. But oysters, it turns out, are difficult to identify based on their shells alone, even for the experts. The researchers unknowingly came home with a new batch of Pacific oysters. 

These became the beginnings of a new “Midori” lineage, named for Japan’s Midori River, from whose estuary many of the new oysters were collected. Though their arrival was inadvertent, California’s growers were excited to have them: Since these oysters’ Japanese home was further south of the Miyagi Prefecture, they were adapted to warmer waters — meaning they might be better prepared for the future conditions in California. Researchers at Oregon State bred several generations of Midori oysters under quarantine conditions; finally, in 2016, their descendants were ready to be introduced into U.S. broodstock programs.

By then, more potential upsides had been revealed. “A lot of folks in Tomales were really excited about Midoris, because they seem to be a little bit more resistant to OsHV-1,” says Johnson, referring to a virus that can strike oysters in warmer waters and weakens their immune system, making them susceptible to diseases and mass die-offs. Hog Island Oyster Co.’s hatchery began to breed and outplant pure Midori oysters, pure Miyagi oysters and a hybrid of the two lineages, hoping to study how each performed.

Expanding the data

California Sea Grant started assisting on the project in the spring of 2024.

“We've been studying these different lineages to try to understand — how do they grow? How do they survive?” Johnson says. Oyster seed from Hog Island has been planted at several farms in different California estuaries: Tomales Bay, where Hog Island has its commercial operation; Humboldt Bay, the site of the company’s nursery; Morro Bay; and, a new addition this year, Eld Inlet in Washington. 

Oyster farmers such as Hog Island are looking for oysters that ideally not only survive well but also grow fast. "Those are the big buckets we're trying to fill," says Hog Island's Fleener. "And we do see differences between lineages."

To help oyster farmers decide which seed are the most promising, each month, 72 oysters from each of the four estuaries are shipped to Johnson’s laboratory at California Polytechnic State University San Luis Obispo, where, working with graduate and undergraduate students, he takes a series of measures to see how they are developing. Besides growth rate and survivorship  Johnson’s team is also looking at “meat weight” — “a pretty important commercial metric,” he notes. “It’s one thing to have an oyster with a big shell and another to have a nice, meaty oyster.”

To find the meat weight, Johnson’s students open the oysters to weigh the meat twice — first while still wet and then again after it’s spent three days in an oven, at about 350 degrees Fahrenheit, to bake out the water. The ratio of meat weight to shell weight is what’s known as the “meat-index ratio.”

This year, Midori oysters have shown a high meat-index ratio. “But that’s not necessarily a great thing in this case,” Johnson says: part of that extra weight is due to the presence of reproductive organs, which can give oysters a milky texture. Typically, the gonads are only present in oysters during breeding season, but it seems this year, the oysters missed some environmental clue to reabsorb their reproductive organs, making the Midoris “maintain their gonads all year, which isn’t always a great thing for marketability.”

An unexpected payoff

Johnson notes that these results are just from one year — too short a period to make any grand conclusions. In other words, further study is important. But even if Midori oysters are not the final solution for Pacific oyster aquaculture in California, his team’s research has already proved its utility.

For example, the study has prompted Hog Island to rethink some fundamentals of its oyster rearing strategy. After noticing how much better the oysters used for the study survived compared to other oysters on the farm, the company is re-evaluating its stocking practices, says Fleener. "We stock the oysters in the study baskets at a very moderate density. We tend to stock more heavily on the farm. And we think that higher stocking density on the farm may be taxing us in terms of survival," he says. The company is now experimenting with lowering its farm stocking rates "to see if we can increase survival by turning the density knob," says Fleener.

Another partner, the Morro Bay Oyster Company (MBOC), gained an even more unexpected benefit from the study. MBOC sends Johnson oysters each month for analysis. "It's been amazing to have somebody craft a study whose answers could possibly help the industry," says company owner Neal Maloney.

But even in the short term, Johnson's data has already saved MBOC some serious money. Last year, the company decided to increase the number of oysters under production. Normally, that would have meant building a new wet-storage facility since the permits supplied by the Department of Public Health only allowed the company to store a specific count of oysters in each facility, and it was about to exceed its limit.

However, MBOC was also shifting toward smaller oysters. This is a market-driven decision, Johnson says: Restaurants used to sell oysters that were three-and-a-half to four inches long; lately, though, diners have been seeking smaller, two-and-a-half-inch oysters.

“They called me and said, ‘Hey, can you help me think about this?’” Johnson says. Thanks to the research he’d been doing, Johnson could do more than think about it: He could run the numbers. He was able to calculate the overall volume of a two-and-a-half-inch oyster grown on the farm — which helped show that there was plenty of room in the existing wet-storage facility still. “I wrote up a brief one-pager with some of the formulas, and it's now Appendix B on their permit,” Johnson says.

"The health department was blown away because within an hour I had a letter from Kevin that laid out all the calculations for the volume of our shellfish," Maloney recalls. "Within a day, the health department had changed my capacity." Maloney estimates that this saved MBOC "a couple of hundred thousand dollars" in costs and maybe a year in construction. "It is a massive bonus for our business," he says.

For Hog Island's Fleener, the oyster seed study is just one example of how important the extension service provided by California Sea Grant is to the industry. "As we shellfish farmers try to use science to do better, to practice better farming and to have a better business, the consultation and collaborative work we do with Sea Grant is invaluable to our success."