Report: Most local fish, shellfish harmless in moderation

A new study assessing mercury accumulation in local fish and shellfish found most nearshore coastal species are safe to consume in moderation — with a few exceptions.A new study assessing mercury accumulation in local fish and shellfish found most nearshore coastal species are safe to consume in moderation — with a few exceptions.

The study, conducted by Humboldt Baykeeper between 2019 and 2020, took a look at the mercury levels in 70 individual fish across nine species including lingcod, several species of rockfish as well as Pacific and California halibut.

“This is our second study and we focused on fish caught in nearshore areas between Reading Rock and Cape Mendocino whereas our first study focused on fish caught in Humboldt Bay,” said Humboldt Baykeeper director Jennifer Kalt. “Pacific halibut was one species that a lot of the sport fishers wanted us to focus on because it’s such a popular fish, people are catching the living daylights out of it right now.”

The good news is Pacific halibut showed fairly low levels of mercury, Kalt said.

“We didn’t have enough samples of California halibut last time so we just wanted to be sure,” she said. “We also wanted to sample more lingcod because what we found in the first study was that smaller lingcod had lower levels of mercury which is pretty standard. It’s generally safest to eat smaller younger fish.”

The California Environmental Protection Agency awarded Humboldt Baykeeper $40,365 in June 2019 to test Pacific lamprey, lingcod, halibut, black rockfish and other fish species for mercury.

A previous grant from the state EPA allowed Humboldt Baykeeper to assess the mercury content in coastal fish and shellfish and put out guidelines regarding which ones are safest to eat.

“From that study, we had a lot of good news and bad news,” Kalt said during a July 2019 interview with the Times-Standard. “Chinook salmon are very low in mercury, so you can eat those up to 28 times per month. That’s good for tribal members because that amount is consistent with the amounts of fish they might eat.”

Back in 2012, a coastwide sampling across California found the highest mercury levels in the state in a leopard shark from Humboldt Bay.

“ The 2012 findings prompted us to do this study. We were pretty alarmed when that study came out,” Kalt said. “They had also tested some rockfish and so we expanded on that and tested a bunch of different rockfish which are generally long-lived bottom feeders. Most of them are pretty high in mercury, the exception to that is black rockfish — which people also call cod or sablefish — which are safe to eat two to three times a week.”

Mercury exposure can lead to a variety of negative health effects, ranging from severe to subtle. Pregnant women are advised to pay attention to their fish consumption because mercury is easily passed from the mother to the unborn child, leading to possible issues with brain and nervous system development.

Fortunately, mercury levels in an individual’s bloodstream will decrease if they stop eating fish.

“If you change what fish or meat you’re eating to lower your mercury exposure, your body will have lower levels within just three months,” Kalt said. “A lot of people — myself included — assumed that it was like dioxins and PCBs (polychlorinated biphenyls) where once you have it in your body it’s just a permanent burden for the rest of your life. That’s not the case with mercury.”

During the 2018 study, Humboldt Baykeeper interviewed 80 fishermen, including one from Shelter Cove who suffered mild health effects from elevated mercury levels who had been eating local rockfish three to four times a week, Kalt said. Within three months of changing his eating habits, his mercury levels decreased.

As a rule of thumb, Kalt said it is generally safest to eat smaller, younger fish.

“The longer the fish lives the more toxins accumulate,” she said. “…There’s also a lot less fishing pressure on the North Coast than there is in areas like Southern California or the Bay Area. They’re catching younger, smaller fish. We have bigger, older fish here because there are just fewer people out there fishing and harvesting those older fish on a regular basis.”

The fish that were tested were all above the legal size limit, Kalt added.

“We were only testing fish that people would actually be eating,” she said. “A lot of fishermen throw back the biggest fish anyway because they’re just not as good to eat. In a way, it’s good for fish populations as well because those bigger, older fish are better at reproducing.”

That being said, leopard shark and lingcod over 20 pounds should be avoided by everyone, regardless of age and gender, according to the study. Lingcod and many rockfish species under 10 pounds and 28 inches are safe to consume once a week.

Humboldt Baykeeper’s 2021 study can be found at

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