Should The ‘Exciting’ New UH Research About Mercury Levels In Fish Caught in Hawaiian Waters Concern You?


It’s not everyday that we get a press release that contains the words “exciting” and “mercury” in the same sentence. But that’s what happened a couple weeks ago, and we have the University of Hawaii public information office to thank for it.

“Mercury–a common industrial toxin–is carried through the atmosphere before settling on the ocean and entering the marine food web,” stated the Aug. 26 press release. “Now, exciting new research from the University of Michigan and the University of Hawaii at Manoa School of Ocean and Earth Science and Technology (SOEST) combines biogeochemistry and direct marine ecology observations to show how the global mercury cycle is colliding with ocean fish–and the human seafood supply–at different depths in the water.”

In a state where the consumption of seafood is both big business and an old tradition, talking about the accumulation of mercury in fish–which, like climate change, is a direct result of industrialization–is difficult. Especially when some of the finest, most delicious and expensive fish served on the island turns out to have the highest mercury concentrations.

While scientists have known that certain types of fish carry a good deal more mercury in their flesh than others for some time, they haven’t really understood why. The new “exciting” research that prompted the Aug. 26 UH press release begins to unlock that why, though it also points the way to new unknowns.

The study examined why fish that live deep in the ocean have higher mercury levels than those living at shallower depths. It turns out, according to one of the UH researchers, that the sun has a great deal to do with why that happens.

“In surface waters, sunlight destroys organic mercury,” said Dr. Jeffrey Drazen, an associate professor of oceanography at the University of Hawaii who was one of the researchers in the new study. “That doesn’t happen down deep.”

Drazen is an ecologist. He studies the ecology of deep sea fish, and for him, this is truly an “exciting” study. “I think it’s good news in our understanding the ocean, how mercury gets into fish,” he said. “This study took about two years. But we’ve been looking at mercury in deep water around Hawaii since about 2007.”

And for those who love mahi mahi, salmon and other fish that live close to the surface of the ocean, this is indeed “exciting” news. But for those who enjoy dining on swordfish, opah, monchong and walu, it’s anything but.

“I love swordfish,” Drazen told me, and he’s certainly not alone. All those fish are delicious, and pop up here and there as specials (and menu items) at some of Maui’s finest restaurants.

Son’z Maui at Swan Court in Ka‘anapali has served macadamia nut crusted opah. Nick’s Fish Market in Wailea offered a candied peanut crusted Hawaiian opah. Mama’s Fish House in Kuau has a lovely Opah sautéed with Hamakua mushrooms, garlic butter, white wine and capers on their lunch menu. And Pineapple Grill in Kapalua has served a Porcini dusted monchong.

Now this is where people who love great seafood–who love great food–should be outraged. These fish–the opah, swordfish and monchong–through no fault of their own, now contain such high levels of mercury that health officials say pregnant women, women who are about to become pregnant and children shouldn’t touch them at all.

After all, we put the mercury there in the first place. And it’s getting worse.

“It turns out that the mercury that enters the ocean comes from the atmosphere,” said Drazen. “It comes from biomass plants. Mercury [levels] from Europe have been going down because there is less reliance on coal there. But in China, India, they’re using more coal plants. Overall, it looks like mercury levels are on the rise.”

Now that’s exciting! But what’s really surprising (or at least what I found surprising) about the new mercury fish study is how it really shows what we don’t know about swordfish, opah and monchong.

“If organic mercury is entering the food web down deep, then we need to look down there to see how they’re getting it,” Drazen said. “We need a better understanding of the food web down there if we want to understand how mercury levels are growing.”

Or put another way: we eat fish like opah, walu and monchong even though we really have no idea what those fish eat. Have we really been consuming fish without any idea as to what they themselves consume?

“We don’t know anything about their feeding habits,” Drazen said.

How could this be?

“The swordfish diet has been studied a little bit,” Drazen said. “Often what happens is that a fishery develops. Then scientists study that species. But when a fishery changes, science takes a while to catch up. It’s a common problem when developing sustainable fisheries.”

Which is what’s going on now. New fish has appeared on our menus, and science is playing catch-up. Though it is a difficult game of catch-up, to be sure.

“If you want to know what something eats, you get a bunch of them and open up their stomachs,” said Drazen. “But It’s not easy studying the deep ocean. We use a very fancy net system to capture animals. We use submarines or remotely operated vehicles. It can be expensive.”

As to what people should actually do with this information, that’s an entirely different question. The good people at the Hawaii Department of Health (DOH) have attempted to answer that question, but the result is far from a conclusive “Don’t eat that!” In fact, fish remains one of those must-eats on most doctors’ lists of what people should consume to help or even avoid heart trouble.

“No one knows what the ‘safe’ level of mercury is,” states a DOH brochure titled A Local Guide to Eating Fish Safely, which kind of calls into the question the whole brochure’s reason for existence.

But first and foremost, the brochure states emphatically that people should most definitely not stop eating fish. “Remember, fish is a good food and part of a healthy diet,” it states. “So don’t stop eating fish!”

This is true for most people, say state health officials. But for young children, pregnant women and women who could soon become pregnant, it’s an entirely different matter. That’s because mercury “bioaccumulates”–it builds in the body over time, which is why those with developing brains are at risk of mercury poisoning. And that’s why the DOH brochure lists a bunch of fish that pregnant women and children need to watch (see accompanying sidebars).

“Mercury can be very harmful to the brain and even small amounts can damage a brain that’s just starting to form or grow,” states the DOH brochure. “That’s why young children, unborn and breast-fed babies are at the most risk.”

As for the rest of us, scientists and health officials really can’t say.

“We don’t have any recommendations for adults,” said Janice Okubo, a spokesperson for the Hawaii DOH. “There haven’t been any issues with people on normal fish diets. Our only recommendation for adults would be that, like anything else, you should eat fish in moderation. Fish is part of a healthy diet.”

Hard answers require hard research. And that, says scientists like Drazen, is still taking place.

*   *   *

Ika (squid)
Fish small enough to fit in a frying pan whole

Kajiki (Pacific blue marlin)
Shutome (swordfish)

Cod (butterfish)
Nairagi (striped marlin)
Orange roughy

[Source: Hawaii Department of Health]