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Evaluation of Mitigation Strategies for Harmful Algal Blooms in the West Coast Dungeness Crab Fishery

This project began in September 2020 and is projected to be completed in August 2024

We will assess the potential economic benefits of mitigation strategies for harmful algal blooms in the Dungeness crab fishery along the U.S. West Coast.

Why We Care
In 2015, the West Coast California Current marine ecosystem experienced a marine heatwave (nicknamed “the blob”) that caused major shifts in the phytoplankton and zooplankton communities at the base of the food web. The blob is believed to have triggered a coast-wide bloom of the diatom Pseudo-nitzschia australis that contaminated shellfish with high concentrations of the toxin domoic acid (DA), forcing closures or delays of shellfish fisheries up and down the West Coast. DA outbreaks often continue to impact benthic organisms long after the toxin-producing species have dissipated. The opening of the 2015–2016 Dungeness crab season was delayed on the West Coast due to high DA concentrations in crab that persisted long after the bloom had ended. The delays were unprecedented in duration, lasting nearly five months in some regions of California.

The Dungeness crab fishery is the most valuable fishery on the U.S. West Coast, with gross revenues for California, Oregon, and Washington averaging over $200 million annually in recent years. It is also one of the largest fisheries in the region in terms of participants, with well over 1,000 permitted fishers. It is the primary source of income for many fishing households. The unusually long delay of the 2015–2016 Dungeness crab season in California led to a request for disaster assistance from the Governor of California based on an estimated $48.3 million in direct economic losses. When the fishery did open, revenue in California was only 52 percent of the average for the prior five years. A key point is that recent losses in the California fishery were not due to direct mortality of crab associated with the P. australis bloom; they arose from the delayed season start that was needed to ensure that contaminated crab was not sold and consumed by the public.

What We Are Doing
The project team will analyze the potential effects of alternative mitigation strategies for harmful algal bloom (HAB) impacts on the West Coast Dungeness crab fishery. The primary focus is on regulatory approaches that are flexible and can increase opportunities for the industry amid HAB events, while ensuring food safety for consumers. Allowing for the harvest and sale of eviscerated crab is one such mitigation policy adopted by Oregon. Since DA in crab tends to be concentrated in the viscera, primarily in the hepatopancreas, eviscerating crab before they are cooked and consumed can make crab safe to eat. In 2018 and 2019, Oregon initially closed some areas of the coast when elevated levels of DA were found in Dungeness crab during the season, but reopened areas under regulations requiring crab from these and surrounding areas to be eviscerated. California and Washington have not allowed landing of crab under evisceration orders to date, but face an increasing need to develop mitigation options to address future HAB events.

Domoic acid concentrations in crab viscera will decline over time if they are held in tanks and not fed, and even more quickly if they are fed uncontaminated food. This suggests holding contaminated crabs in tanks and feeding them might be an effective strategy for mitigation. Mitigation strategies may be more effective if combined with finer scale spatial management informed by HAB monitoring and forecasting data. If concentrations of DA in crab are patchy, it may be possible to continue harvest and sale of whole crab from areas without high concentrations and limit the need to eviscerate or hold crab to areas with high concentrations. This could considerably reduce the resources and labor needed to employ these mitigation strategies. However, it also requires a system of monitoring, regulation, and tracking of harvested crab to ensure crab from areas with high DA concentrations are eviscerated before cooking or are held in tanks.

To determine whether state agencies and the industry should make the investments required to implement these mitigation options, a cost-benefit analysis is necessary. Such an analysis must consider the costs of the mitigation itself (regulatory costs and actual costs of mitigation processes), as well as impacts the mitigation action may have on value (e.g., if eviscerating crab reduces the market value of the crab). Additionally, mitigation strategies should be evaluated against plausible scenarios for future HAB events—including potential duration, spatial pattern, and scale of contamination—in order to bound potential gains this mitigation option would provide. Finally, to quantify the economic value of information provided by HAB monitoring or forecasting capability, it is essential that modeling integrates mitigation strategies and existing fishery management policies with the economic structure of the industry.

Dr. David Kling of Oregon State University leads this project. Co-investigators are Dr. Daniel Holland (NOAA NWFSC), Dr. Sunny Jardine (University of Washington), Dr. James Sanchirico (University of California at Davis), and Dr. Gil Sylvia (Oregon State University). The project is funded through the NCCOS Prevention, Control, and Mitigation of Harmful Algal Blooms Program.

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