Humboldt Baykeeper's second study of mercury in local fish focused on species from nearshore coastal waters. We sampled 70 individual fish across nine species, including Pacific Halibut and several species of rockfish. We also sampled additional Lingcod and California Halibut to add to the data from our 2018 study. We found that most local fish are safe to eat in moderation—with a few exceptions.
Click HERE for revised recommendations on Eating Fish Safely.
Comiendo Pescado Con Seguridad Pautas
Yuav Ua Li Cas Noj Ntses Yam Xyuam Xim Cov Txhooj Cai Rau Humboldt Bay
Our final report, Mercury Testing of Sport/Food Fishes from Nearshore Ocean Waters of Humboldt County, California, is available to download HEREEstudio sobre mercurio ampliado para incluir peces capturados en el océano.
New! Phone-sized images for handy references (click to enlarge or download):
After our 2018 study of mercury levels in fish from Humboldt Bay, people asked us to study mercury levels in popular ocean-caught species like Pacific Halibut. We were fortunate to receive a second grant from the California Environmental Protection Agency in 2019 to study mercury in species caught off the coast near Cape Mendocino, Patrick’s Point, and Reading Rock.
We sampled 70 individual fish across nine species in 2019-20, including Pacific Halibut and several species of rockfish. We also sampled additional Lingcod and California Halibut to add to the data from our 2018 study, Mercury Testing of Sport/Food Fishes within Humboldt Bay. These fish were caught by Ross Taylor and Associates (RTA), a consulting fisheries biology firm, Jeffery Stackhouse, the captain of Stackhouse Guide Service, and their assistants.
Why study mercury in fish? 
Eating fish has health benefits – as long as it is low in mercury, which tends to bioaccumulate in bigger, older fish. Although most mercury exposure in the U.S. is from eating fish, it’s important that people don’t avoid all fish because of the health benefits related to its high protein/low fat content, omega-3 fatty acids, and vitamins A, B, and D – as long as the mercury levels are low.
Mercury is a neurotoxin that is especially harmful to children. It can cause slight decreases in learning abilities, language skills, attention, and memory function. At lower levels, symptoms can include fatigue, muscle and joint pain, memory loss, and numbness or tingling around the mouth. At higher levels, symptoms include loss of coordination, numbness or tingling in the hands or feet, blurred vision or blindness, hearing loss, and speech impairment.
During the 2018 study, we interviewed 80 fishermen, including one from Shelter Cove who suffered mild health effects from elevated mercury levels. He had been eating local rockfish 3-4 times a week. Within three months of changing his eating habits, his mercury levels decreased.
Results & Recommendations for Eating Fish Safely
The U.S. EPA sets lower levels of mercury exposure for children and women of child-bearing age (under 45) than for men and women over 45. Because of the risks to children and fetuses, it is especially important for women planning to get pregnant to lower their mercury exposure by eating low-mercury fish and shellfish.
The good news is that many of the fish caught in Humboldt Bay and nearshore coastal waters have low to moderate mercury levels. However, Lingcod over 10 pounds or 28” long and many rockfish species should not be consumed by women under 45 and children, whereas Lingcod under 10 pounds or 28" long are safe to eat once a week. Leopard Shark and Lingcod over 20 pounds should be avoided by everyone, regardless of age and gender. They are long-lived predators that eat high on the food chain, bioaccumulating high levels of mercury and other toxic chemicals like PCBs and dioxins.
General tips for choosing low-mercury fish are to mostly eat smaller, younger fish or shellfish like crabs, oysters, clams, and mussels. A good general rule when eating fish from a store or a restaurant is to only eat one serving of fish per week, unless you know it is high in mercury or other contaminants and should be avoided entirely.
Mercury in Humboldt Bay
In 2012, a state agency reported on its survey of contaminants in coastal fish. The highest mercury levels in California were found in Leopard Shark from Humboldt Bay. High mercury levels were also found in Copper, China, and Gopher Rockfish caught along the North Coast. This report raised some red flags and led to our pursuit of grant funding for a more in-depth  study of mercury in local fish.
The source of mercury in Humboldt Bay is unknown, other than atmospheric deposition from coal-fired power plants around the world. High mercury levels have also been found in Largemouth Bass in Ruth Lake (Study Finds High Mercury Levels in Ruth Lake Fish,  Oct. 2010 EcoNews). The early gold miners used mercury in the Klamath, Trinity, and Russian River watersheds, but its use is not documented within the Mad or Eel Rivers, which are more likely to deposit sediment in Humboldt Bay. 
Our deepest thanks go to the California Environmental Protection Agency’s Environmental Justice Small Grants Program for funding this research. Thanks to the Cereus Fund of the Trees Foundation and Humboldt Area Saltwater Anglers for additional funding. 
Thanks to all of the contributors who were essential to the success of this project!