Warning on shellfish as bloom hits record level

By DANIEL JACKSON

Health authorities in Northland have issued an urgent warning against eating shellfish after new sea water samples revealed record toxic algal bloom levels.

The tests were done on water sampled near Dargaville.

Algal levels were seven times any previously recorded.

Although results on the toxicity of shellfish meat are not yet known, Northland Health is urging people not to take shellfish from areas around the North Island where warnings are in place.

Eating the flesh was likely to lead to potentially fatal paralytic shellfish poisoning (PSP), it said.

Warnings cover a zone around the North Island extending south from Mahia Peninsula, northern Hawkes Bay, to Cook Strait, and then up the West Coast to Cape Reinga in Northland.

The only region within the zone not totally included is the inner part of the Kaipara Harbour, where shellfish, apart from green mussels and tuatua, can be taken east of Pouto and South Head.

Paua, crabs and crayfish can be taken from the danger areas but the gut should be removed before they are cooked.

Symptoms of PSP include numbness and tingling around the mouth, face or extremities, difficulty swallowing or breathing, dizziness, double vision and paralysis.

The shellfish coordinator for Northland Health, Tony Beauchamp, said samples of water taken from surf at Glinks Gully, south of Dargaville, showed levels of the algae gymnodinium catenatum not previously seen in New Zealand.

The levels suggested that shellfish from the same area, which feed by filtering the water for nutrients, were contaminated.

"They're extremely likely to have been feeding on it."

Northland Health had also heard of people becoming sick after eating only small amounts of shellfish from the area.

Results of phytoplankton samples collected indicated 276,000 cells of the algae per litre of water, which was seven times higher than any other samples of the algae recorded since the bloom was first identified in June.

"It's far denser than we've ever seen before."

Mr Beauchamp said that dead fish were also washing up on beaches, which was a sign the bloom was stronger offshore and robbing the waters of oxygen.

The last recorded example of the bloom killing fish was in Mexico, where the strength was 1.25 million cells per litre of water.

Mr Beauchamp said earlier tests had shown levels were decreasing and it had been hoped the algae, which preferred temperate waters, would go away over the summer months. That was now unlikely.

"It's back with a vengeance."

Mr Beauchamp said the spread of the bloom was difficult to predict.

Dr Hoe Chang, a marine biologist for the National Institute of Water and Atmospheric Research, said not enough was known yet to say why the bloom had grown.

Possible causes included cold water from the ocean bottom rising to the surface carrying nutrients which the bloom fed on, or a concentration of a bloom farther out to sea being blown in to shore.

"But it's all pure speculation at the moment."