Spring Break, Low Tides, and Clam Diggers Makes Shellfish Monitoring in Oregon Important

The ODA routinely monitors shellfish for two toxins: domoic acid and paralytic shellfish poisoning.

(NEWPORT, Ore.) - The arrival of spring, with low tides and potentially good harvest conditions along the Oregon coast, is expected to bring out eager clam diggers over the next few weeks, all the more reason for the Oregon Department of Agriculture to continue monitoring shellfish for marine toxins.

Currently, all beaches are open for recreational razor clamming. But that can always change over the course of the next few months.

"We routinely monitor shellfish for the two toxins of concern – domoic acid and paralytic shellfish poisoning (PSP)," says Deb Cannon, manager of ODA's Shellfish Program. "We have gone almost six months now without any closures due to elevated toxin levels. That's good news for diggers."

While PSP is not a concern this time of year, domoic acid has often forced harvest closures in both the spring and fall. Domoic acid is a naturally occurring toxin produced by marine phytoplankton or algae.

Eating shellfish contaminated with low levels of domoic acid can cause minor illness within minutes to hours after consumption.

In mild cases, symptoms can include vomiting, diarrhea, abdominal cramps, and headache.

More severe cases of domoic acid poisoning can result in memory problems, damage to the central nervous system, renal failure, and even death.

Young children, pregnant women, and the elderly are especially vulnerable to the effects of domoic acid poisoning.

Anyone experiencing such symptoms after consuming razor clams should contact a physician.

Razor clams are affected by domoic acid to a greater extent since the toxin can be stored in the fatty, edible tissue.

While other shellfish, including other types of clams, are able to purge the toxin in a relatively short time, domoic acid is retained by razor clams, making them the target of beach closures when toxin levels are high.

“If we didn't monitor shellfish for these toxins, we would always be reacting to a problem that had already occurred,” says Cannon. “We would have to wait until somebody actually got sick before closing the harvest. Because of our ongoing sampling and testing program, we can take action before anyone gets ill.”

Samples are collected by staff from ODA, the Oregon Department of Fish and Wildlife (ODFW), and a team of volunteers that are especially valuable in gathering shellfish from remote areas of the coast.

"One of our star volunteers gets samples from the North Umpqua spit down near Reedsport, and makes a 40 mile round trip in a jeep out on a sandy beach," says Cannon. "He has to dig for the sample, pack it up properly, take it to a bus station, and ship it to the ODA laboratory in Portland for analysis. This is all part of the system of monitoring the beaches and getting the results in time to ensure it is safe for people to dig for clams. The volunteers are crucial for us."

Other tools of determining what is going on with toxin levels include phytoplankton monitoring -- a relatively low-tech method of sampling.

Simply put, plankton nets are dragged through the water at four or more collection sites on the coast gathering and concentrating the algae in the bottom of the net.

The concentrated level is then observed under a microscope to identify whether it is the type of algae that produces either PSP or domoic acid. ODA and ODFW team up to provide this invaluable monitoring tool.

"This gives us a screening tool that indicates a harvest area that may soon need to be closed down because of an expected appearance of elevated toxin levels," says Cannon.

Domoic acid levels can rise relatively quickly when the harmful algae is present.

Last April, levels jumped from 11 to 60 parts per million in just five days. Levels above 20 parts per million are considered above the safe level and lead to shellfish harvest closures.

Since it can take up to three days following sample collection for the laboratory analysis to be completed, there is always a chance that a recreational harvester may get a clam with an elevated toxin level before the ODA results are known.

But the Shellfish Program monitors trends and uses a safety cushion of sorts to protect the public.

Even though samples with domoic acid levels above 20 ppm trigger a closure, it actually takes levels about three or four times that amount to cause illness in people who consume the clam.

The toxin levels don't spike that high in less than three days without some kind of advance warning. Weekly monitoring maintains public confidence.

Commercial shellfish harvesters are also affected by closures. ODA monitors toxins for all commercial shellfish so that razor clams harvested and then sold to restaurants and other commercial outlets are safe for consumers.

ODA will hold shipments of razor clams if test results indicate toxins are nearing the closure level.

Finally, clam diggers must be aware of the latest conditions and test results. If a beach is closed due to marine toxins, they need to heed the closure.

"People should continue with their plans to go to the beach over the next several weeks and do some digging," says Cannon. "But even on the day they head for the coast, they should check with us for the current status. Domoic acid levels can quickly rise during the spring and fall."

A combination of testing the water before testing the meat of the shellfish should greatly enhance efforts to keep shellfish safe for both commercial interests and the very popular recreational harvesting.

"This is the time of year when interest in clam digging starts to pick up," says Cannon. "The surf is calmer, the tides are getting lower, and the low tides are in the daytime."

Consumers should know that someone is watching out for them when it comes to shellfish safety.

For current information, call ODA's shellfish safety hotline toll free at (800)448-2474.