A single Dungeness crab whose guts were loaded with a pesky biotoxin has put the kibosh on sport and commercial crabbing on the Southern Oregon coast while the rest of the state is open for capturing Oregon’s favorite crustacean.

Tests on crab sampled Dec. 30 showed a single Dungeness taken between Gold Beach and Cape Blanco north of Port Orford showed unhealthy levels of the biotoxin domoic acid, the bane of Oregon shellfish fisheries in recent years.

The discovery triggered the closure Friday of the recreational ocean-crabbing fishery in bays and the ocean from Bandon south to the California border and pushed waters south of Cape Arago off Sunday’s planned start to Oregon’s long-awaited commercial crabbing season.

The season could have started as early as Dec. 1, but concerns about the meat content of Dungeness, as well as domoic acid levels, halted the start of the commercial season until Jan. 15 north of Cape Arago near Charleston.

The toxin, which can cause illness in people, was found above health thresholds in one Dungeness out of the six sampled in the zone immediately north of Gold Beach, according to Oregon Department of Agriculture records.

“All it takes is one crab,” said Caren Braby, the marine resources program manager for Oregon Department of Fish and Wildlife.

The crab tested at 35 parts per million of domoic acid in its viscera, or “guts,” Oregon Department of Agriculture statistics show. The health threshold is 30 parts per million.

Another Dungeness in that area tested at 20 parts per million and another at 12 parts per million, ODA records show. One in the zone from Gold Beach to the California border tested at 18 parts per million.

ODA breaks the Oregon Coast into 12 zones for crab testing. If one zone has a domoic acid level above the health limit, then the zone immediately to its north and south also will be closed, according to the agency.

Since the single crab in the Cape Blanco to Gold Beach zone exceeded levels in the Dec. 30 sample, the recreational closure was extended from Cape Blanco to the California border.

Likewise, the commercial delay was from Cape Arago to the border.

Adding adjacent zones to closures is done because Dungeness are highly mobile and can travel quickly.

The northern end of the commercial and recreational closures differ because the zones are slightly different for each category, Braby said.

New samples were planned last weekend, but bad weather kept boats at bay, Braby said. More sampling is targeted for later this week, she said.

The news was a blow to South Coast crabbers hoping to join their North Coast brethren in Sunday’s opener of Oregon’s most lucrative commercial fishery that last year netted more than $91 million of Dungeness to processors.

For the recreational season to reopen, lab tests must show two consecutive samples that meet ODA thresholds for domoic acid, and those tests must be at least one week apart.

Also, lab tests for adjacent zones must meet safe domoic acid levels, according to ODA protocols.

Domoic acid is a naturally occurring toxin produced by microscopic algae.

The algae concentrates in shellfish, and the acid can trigger amnesic shellfish poisoning in people. Symptoms include vomiting, nausea and abdominal cramps within 24 hours of ingestion.

Mark Freeman covers the environment and outdoors for the Mail Tribune. Reach him at 5431-776-4470 or email him at mfreeman@rosebudmedia.com.