Flooding mooted as cause of shellfish toxins, Hawke Bay collection ban may last weeks or months

Flooding could have contributed to paralytic shellfish toxins affecting much of the Hawke’s Bay coastline.

New Zealand Food Safety (NZFS) extended a previous public health warning not to collect or consume shellfish from Hawke Bay (Cape Kidnappers to Mohaka) and all the way up to East Cape this week.

The warning includes mussels, oysters, tuatua, toheroa, cockles, scallops, catseyes, kina and all other bivalve shellfish.

It came after shellfish collected from Tolaga Bay showed toxins 11 times over the safe level.

NZFS deputy director-general Vincent Arbuckle says various factors cause the floating algae that produces the “dangerous” paralytic shellfish toxins.

“There’s been a lot of flooding in the region, which may have introduced a lot of nutrients into the water to help these blooms thrive,” Arbuckle said.

Commercial shellfish harvesting in the area between Cape Kidnappers and East Cape has ceased, along with Northland and Queen Charlotte Sound, where the toxins are also prevalent.

How long commercial and recreational fishers need to avoid shellfish in this area is hard to say.

“These blooms can last several months, so it could be at least three to four weeks before we can even look at removing the public health warning for some areas,” said Arbuckle.

“We will keep monitoring sites along the coastline and reduce the size of the warning as soon as we can, once we know the bloom has gone and the level of toxins is below the safe limit.”

The issue is a microscopic phytoplankton called Alexandrium pacificum, which is photosynthetic and more common in spring and autumn. When shellfish filter feed, they accumulate the algae and toxins.

This does not affect finfish and pāua, crab and crayfish, provided the gut is completely removed prior to cooking.

Hamish Bidwell joined Hawke’s Bay Today in 2022 and works out of the Hastings newsroom.