Environmental Effects on Washington Crab


The Dungeness crab fishery is one of the most important commercial fisheries in Washington State. During the 2015-2016 season, 11.9 million pounds of commercial state crab were caught off the Washington coast. In Puget Sound, another 3.1 million pounds of commercial state and 5.9 million pounds of treaty crab were landed this season, according to the most recent data from the Washington Department of Fish and Wildlife (WDFW).

Like the salmon fishery, the Dungeness crab fishery is divided into state and tribal fisheries. In Puget Sound, there is an equal allocation between the two quotas. The state quota is further split by the WDFW into commercial and recreational. The tribal crab quota is about 95 percent commercial.

The commercial Dungeness state fishery this year had an ex-vessel value of $57.1 million. The total Puget Sound tribal ex-vessel value is not readily available, but an estimate, based on the $4.58/pound state season average, puts it around $27 million.

The Dungeness coastal commercial state fishery supports 228 license holders. The Puget Sound commercial state fishery has an additional 134 license owners, most of whom have one or two licenses. The data for tribal crab fleet is not readily available and varies from year to year, but an estimate for commercial Puget Sound crabbers is 600 to 800, according to Don Rothaus with the WDFW.

Most commercial state fishing takes place in the first two to three months after the fishery opens in October in Puget Sound and in December on the coast. Dungeness crab price is lowest at the beginning of the season, before the demand ramps up with increased supply. This gives seafood distributors an opportunity to buy the bulk of the crab at a lower price to freeze and supply the market throughout the year, according to the Chinook Observer. Any significant delay in the fishery can thus have reverberations throughout the supply chain, affecting not just the fishermen but wholesalers and restaurants.

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Outside of the market forces, environmental concerns create unpredictability for the Dungeness crab fishery. The main culprits are ocean acidification and coastal algal blooms.

Ocean Acidification

A study published this April looked at the potential impacts of ocean acidification on the development of Dungeness crab. It was a collaborative project between NOAA and researchers from the University of Washington. Jason Miller and co-authors looked at the Washington State coastal and Puget Sound projected pH levels and what they could mean for Dungeness crab larvae.

The current mean coastal pH level is 8.0. Puget Sound has a lower pH and it’s quite variable, fluctuating between 7.6 and 8.1, but predicted to decrease to a low of 7.1 by 2100.

Why do we need to be concerned about a pH change of just 0.5? pH is a measure of how acidic or basic water is. The scale goes from 0 to 14, where 7 is neutral. Distilled water has a pH of 7. The smaller the number below 7, the more acidic water is. The higher the number above 7, the more basic it is.

The pH scale is logarithmic, meaning a change from pH 7 to pH 6 is a 10-fold change. (Compare that to a linear scale, where a change from 7 to 6 is a 1-fold change). Remember, the lower the number the more acidic a solution is, so a solution that drops from pH 7 to pH 6 is now 10 times more acidic.

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Our healthy blood pH level is between 7.35 and 7.45. If our lungs cannot remove enough carbon dioxide produced by our body, too much of it will accumulate in the blood. Increased carbon dioxide levels will cause the pH of the blood to decrease and become more acidic. If the pH drops below 7.35, it will cause a condition known as respiratory acidosis. An acute form of it can be fatal.

Similarly, an increased absorption of carbon dioxide by the oceans creates a more acidic marine environment.

While corals and bivalves, like oysters and clams, have been getting the most attention from the effects of ocean acidification, there are substantial effects on other animals, including the Dungeness crab. A crab’s shell is made primarily of chitin and proteins and is not affected by bleaching, the way it affects oysters. However, lower pH levels are thought to disturb internal acid-base levels and cause a decrease in the animal’s metabolism, according to the study.

The authors found that at lower pH level crab eggs hatched at a later than normal time. Lower pH also slowed embryonic and early larval development and caused substantial larval die off. These effects, caused by ocean acidification, could have a “deleterious impact on the population.”

The authors point out, however, that the “response to low pH can vary among populations or strains within a single species.” Eggs of Dungeness crab are carried by the female near the ocean floor. Once they hatch, the larvae spend several months in the water column before settling in the near shore as juveniles. Acidity of these environments is substantially different from each other. So the crab are exposed to a variety of pH levels throughout their development due to their life history and geographic distribution from Alaska to California.

Chris Long, a researcher with the Alaska Fisheries Science Center in Kodiak, Alaska studies the effects of ocean acidification on king and Tanner crab. At a recent Bering Sea Fisheries Conference in Seattle, he pointed out that “laboratory experiments almost always overestimate the effects.” Looking at the laboratory experiments over many different species and years, he concludes that they are good at predicting the direction of the change but can exaggerate its magnitude.

In addition, Long said, there are natural forces that might help a species to cope. Animals in general have plasticity – they can adjust their body chemistry to stressors in the environment. Ocean acidification will also take place over many decades, giving the crab time to adapt and evolve over multiple generations.

Still, it is important to monitor and understand how the environment and the species are changing. The better we understand the patterns of change, the better we can anticipate and prepare for the fishery disruptions that lie ahead.

Algal Bloom

How does an organism no longer than 0.007 inches shut down a multi-million dollar fishery from California to Washington? Through sheer numbers and a defensive toxin.

The tiny organism is Pseudo-nitzschia, a diatom, popularly called algae, one of the most common groups of the phytoplankton. Phytoplankton are microscopic plant-like organisms that absorb nutrients from the ocean, in turn producing oxygen, much like plants do on land. About half of the oxygen we breathe comes from the phytoplankton. Tiny animals called zooplankton feed on the phytoplankton. Juvenile fish, small adult forage fish, like herring and anchovies, and some shellfish in turn feed on the zooplankton.

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There are thousands of species of phytoplankton and Pseudo-nitzschia is just one of them. On occasion, these algae can produce domoic acid. It’s a toxin that in people causes the amnesic shellfish poisoning, also referred to as domoic acid poisoning, according to the Northwest Fisheries Science Center (NFSC) website.

During the algal high-growth phase – an algal bloom – zooplankton will consume many of these organisms. In turn, zooplankton-feeding fish and shellfish will consume thousands of these zooplankton. Animals higher on the food chain accumulate more of the domoic acid toxin. Adult Dungeness crab will scavenge for algal and animal matter on the bottom, where the concentration of the domoic acid is even higher. This is called bioaccumulation.

The Pseudo-nitzschia-fed zooplankton, fish and shellfish don’t seem to have visible ill effects from the toxin, according to the NFSC website. However, for animals higher on the food web, like sea mammals, birds and us, the toxin can have deleterious effects from too much consumption. In humans, high-enough doses of domoic acid can cause permanent brain damage, including short-term memory loss, and on a very rare occasion, death.

The 2015 Pseudo-nitzschia algal bloom was unprecedented in its scope and duration. Algal blooms occur naturally when cold, nutrient-rich deep water is brought to the surface in the spring, providing nutrients for phytoplankton to flourish. Normally, these blooms last only a few weeks.

Last year, an unusual warm water “blob” created a record-breaking algal bloom of at least the last 15 years, according to NOAA News. “We had two pools of warm water hitting the coast in the Pacific Northwest and southern California and merging, so all at once there were warm waters over the whole west coast,” UC Santa Cruz professor Raphael Kudela said on the university news website. The bloom stretched from California to Alaska. According to the WDFW, higher domoic acid levels were detected in parts of Washington well into the winter and spring of 2016.

The Power to Act

Ocean acidification and extraordinary toxic algal blooms are big problems that will require the cooperation of many different entities. They are expected to affect the fisheries during the next few years and into the conceivable future.

HR 2553, or the “Coastal Communities Ocean Acidification Act of 2015”, is a piece of legislature currently being considered that specifically directs NOAA to “conduct coastal community vulnerability assessments related to ocean acidification.”

According to Ryan Ono, manager of the Ocean Acidification Program at the Ocean Conservancy, “more specifically, the bill directs NOAA to conduct socioeconomic vulnerability studies of ocean acidification impacts on coastal and island communities. These studies would help identify which communities are most dependent on ocean resources and how acidification would affect them if valuable industries, such as Dungeness crab, were affected. The bill further encourages non-federal employees, such as Dungeness crabbers, resource managers, and scientists to investigate acidification and its local impacts.”


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