Crabs and Domoic Acid

Jimmy YarnallCrab and Shellfish

Jimmy YarnallUnless you’re lucky enough to have been on an extended out of state hunting trip or vacation, you are well aware of the statewide delay of the recreational Dungeness crab season. The following is a brief summary of the issue to date.

Domoic acid is naturally occurring neurotoxin produced by phytoplankton. Phytoplankton blooms are affected by water temperature, nutrient levels, currents, and other unknown factors. When organisms consume phytoplankton and are then preyed upon by other organisms, domoic acid becomes concentrated as it moves higher up the food chain. By the time a crab feeds upon dead anchovies or razor clams, the domoic acid level in the crab’s food may have increased substantially over levels present in the surrounding environment, having been concentrated at each trophic level. Crabs with high acid levels appear to suffer no ill effects, but problems occur when mammals consume crabs or other organisms with concentrated acid levels.

The effects of domoic acid poisoning in humans include a wide range of symptoms from short-term memory loss, brain damage, and, in severe cases, death. The most significant recent case of poisoning occurred in 1987 on Prince Edward Island where numerous patients exhibited serious symptoms and three fatalities were reported as a result of the consumption of blue mussels.

Various California state agencies were aware of high domoic acid levels in crab and razor clams in Washington that caused season closures earlier this year and were monitoring the situation within California waters. Health advisories were issues regarding rock crab and razor clams within certain areas of the state. With the opening of both the recreational and commercial Dungeness crab seasons looming, the state recently completed one last round of sampling and testing from Crescent City to Morro Bay before the recreational season was scheduled to begin. The results still indicated that high levels of domoic acid remained in most sample areas. The state then took action to delay the opening of both the recreational and commercial seasons until the levels drop below threshold levels safe for human consumption. Testing continues on a weekly basis.

The state of California has not dealt with this issue previously, and the agencies involved are doing their best to accurately monitor the situation, provide fishing opportunities as soon as possible, and most importantly, to keep the public safe. They do not, however, have a playbook from previous years’ experience but instead are working closely with their counterparts in Oregon and Washington. Currently the commercial seasons remain closed in all three states. Oregon estuaries are open for crabbing north of Heceta Head (Florence) where acid levels have dropped below advisory levels.

The real question everybody wants answered is when and how the season will open in California. My response is that nobody knows for sure. Results from studies in Washington illustrate that it takes considerable time for acid levels to drop within the crab muscle tissue, even after the crab are eating “clean” food free of domoic acid. My personal guess is that it will likely be after Christmas before we can go crabbing on the North Coast. Acid levels in areas to our south appear be dropping more rapidly. The California Fish and Game Commission has indicated that it intends to open recreational crabbing regionally as areas become safe and to do so prior to the commercial season. To date, the commercial crabbers are in favor of a statewide opening when all areas are deemed to be safe. How this will all play out is anybody’s guess.
Below are some links to several sources of information that you may find helpful and interesting.

CA Dept. of Public Health

CA Dept. of Fish and Wildlife

Oregon information