Concern another poor Bluff Oyster season may be looming

Friday, 10 February 2023

Bluff Oyster fisherman Willie Calder, on board his boat Argosy ahead of the 2023 season, says dry summers aren’t generally ideal for oyster growth.

Industry experts are concerned the wild Bluff Oysters in Foveaux Strait may be of poor quality for the second year running.

The season kicks off on March 1 and an assessment of the fishery is to be done next week.

Longtime oyster fisherman Willie Calder has expressed concern the oyster quality may be similar to last year, when smaller oysters were dredged from the ocean floor.

“Last year we had a drought and the oysters weren’t in very good order, and the way this year’s weather has gone, it could be similar.”

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“I’m always hopeful, but the signs don’t look very good.”

Oysters lived off phytoplankton which was the “grass of the sea”, and it didn’t thrive in drought years, he said.

Bluff Oyster fisherman Willie Calder prepares his boat Argosy [behind] for the 2023 season which begins on March 1 in Foveaux Strait.

In years of heavy rainfall the oysters tended to be of good quality, he added.

“When Invercargill flooded in the early 1980s, that’s the best oysters I have ever seen. They were bursting out of the shells they were that fat.”

Calder is the owner of the Argosy oyster boat and approaching his 49th season catching the delicacy in Foveaux Strait.

“You have to take the good [seasons] with the bad.”

Barnes Oysters manager Graeme Wright said the quality of the wild Bluff oysters had not been checked this season, with an assessment of the fishery to begin at the end of the week.

He also was concerned they may be small again.

“We all want nice big fat juicy oysters, don’t we, but it is mother nature, it’s a wild fishery. Hopefully they will be better than last year, when certainly the quality wasn’t good.”

Last season was the poorest quality oysters he had seen in the 26 years he had been in the industry.

The 2021 Bluff Oyster and Food Festival was a success in the deep south. [File video].

On a positive note, there were vast quantities of baby oysters in the strait, and background levels of the oyster killing bonamia disease had been very low in Foveaux Strait for the past three seasons.

“There are no issues about the number of oysters out there … it just seems like they need a good feed.”

Oysters could pick up condition quickly if the conditions were right, Wright said.

“We just need the phytoplankton there,” he said.

NIWA principal scientist in Wellington, Dr Matt Pinkerton, confirmed Bluff oysters' main food source was phytoplankton [tiny plants].

Phytoplankton needed sunlight and nutrients in the water to grow, and in times of heavy rainfall many nutrients flowed into the ocean from rivers after washing off the land.

Conversely, Pinkerton said sediments also flowed into the ocean from the land, which could reduce phytoplankton growth due to it reducing the sunlight reaching the tiny plants.

Other factors controlling phytoplankton growth included water temperature, winds, waves and currents.

The changes to ocean conditions could affect animals in the food chain such as oysters, as could pollution, disease, parasites and fishing.

Data was being gathered but was too early to definitively say what was affecting oyster growth rates in Foveaux Strait.

'This will take a dedicated research effort. To answer this, we need to understand how the environment is changing, and link cause and effect.”

NIWA’s work was continuing and data gathered may provide clues, Pinkerton said