PSP toxin, which is naturally occurring and is caused by certain kinds of algae, produces symptoms similar to severe food poisoning: vomiting, diarrhoea, stomach pain and numbness.

James Austin, the president of the Underwater Harvesters Association, representing BC’s 55 licensed geoduck harvesters, said he could not understand why Hong Kong had imposed a blanket ban on the entire province when the toxin had only been found in a single harvest area – one of several thousand in BC waters. Individual harvest areas are only 100 to 200 metres long, but BC has a vast coastline of more than 25,000km.

All harvesting in the affected area was halted after the initial discovery of the toxin, Austin said on Monday.

Particularly galling to BC harvesters is the fact that other exporters have stepped into the gap, including Washington state – whose waters border BC – and Mexico, which Austin said did not even test its clams for PSP toxin prior to export.

Austin said the Hong Kong ban had had a huge impact; the BC harvest is down about 180,000kg compared to this time last year. Boats are lying idle and divers who gather the wild delicacy from the seabed are taking time off work.

“Forty boats up north have just had to have five days off because they haven’t had the ability to sell,” Austin said. Harvesters usually sell the clams for about C$27/kg, but in Hong Kong they retail for much more.

The 55 harvesters in BC represent 120 to 150 direct employees like divers and deckhands, Austin said. However, the ban has also affected businesses and workers further down the supply chain.

“We’ve got workers in Vancouver, at five or six different plants that are slowed down right now, we’ve got trucking companies that are now only trucking 25 per cent of the product that we normally ship…it just escalates,” he said.

Some of the lost harvest could be made up with increased exports later in the year if Hong Kong lifts the ban, but “we would have a difficult time making that up”, Austin said. Missing out on the lucrative Lunar New Year period was a major blow.

Canadian authorities are in discussion with Hong Kong’s Centre for Food Safety (CFS) about getting the ban lifted, but Austin said his organisation had been kept in the dark about the process. Representations made by the UHA to Hong Kong had yielded little response. “It’s been frustrating,” Austin said. “We would like to be involved in the conversation.”

The CFS said it was liaising with the Canadian Food Inspection Agency (CFIA) and the ban would only end once it was satisfied “that geoduck clams from the harvest areas are safe for consumption”.

The CFS said it knew of no reports of food poisoning related to BC geoduck last year.

The CFIA said Hong Kong had asked for a report “explaining why geoducks harvested from open areas were found to contain unacceptable levels of PSP”.

It was only Canada’s toxin-monitoring programme that alerted Hong Kong to December’s PSP-tainted sample, which had 110 micrograms of toxin per 100 grams, compared to the international safety standard of 80 micrograms. Hong Kong then did further tests on the batch that confirmed the Canadian data before instituting the province-wide ban.

The CFIA has since detected three other samples with elevated toxin levels. The agency did not say where these occurred, but Austin said all were found in the same closed harvest area which yielded the original tainted batch. Harvesting was halted in that area in December, and BC geoduck continues to be exported directly to mainland China and elsewhere around the world. It is also being sold domestically.

“The CFIA and the Hong Kong Centre for Food Safety of the Food and Environmental Hygiene Department have been working together to resolve this issue,” the CFIA said.

Mollusc with an indelicate nickname is a delicacy nonetheless

Variously known as the king clam, horse penis or elephant trunk clam, the geoduck is far more palatable than its appearance and some of its nicknames suggest.

Panopea generosa, the variety found in British Columbia, sports an impressive meaty siphon or neck that can stretch more than a metre long. The flesh of the clam is so massive that most of it bulges outside the two halves of its inadequate shell.

To make up for this vulnerability, the clam buries itself deep in the sandy sea floor. Divers must work hard to extract the creature, using a water hose to loosen the sand surrounding the siphon to allow the clam to be pulled free. Although geoduck clams have been known to live up to 168 years - making them potentially prone to overfishing - the BC industry is tightly managed and is endorsed as sustainable by the David Suzuki Foundation and other experts.

The clams are generally exported live, with the animal able to survive for extended periods outside water if treated with care.

The first major overseas market was Japan, where it is known as “mirugai” and is often served as finely sliced sashimi. But Chinese consumers now consume the bulk of the catch. The flesh, which has a crunchy texture when raw, can be stir fried, served in hot pots, seared or made into a soup.

Vancouver chef Stephen Wong says geoduck should never be overcooked and recommends a low heat to “retain its highly desirable sweet flavour”.

The name “geoduck” is a misspelling of its phonetic name in the language of the Nisqually native American people. It is pronounced “gooeyduck”, and is said to be a reference to its penis-like appearance.