Ngāi Tahu holdings chief executive Todd Moyle said for the past two years it had stopped harvesting Bluff oysters, known as tio, earlier in the season due to a decline in the quality and quantity and size of the catch.
While disease and viruses were significant contributors to the decline in healthy tio populations, he said there were other factors negatively impacting the fishery, such as fluctuating sea temperatures and climate change, leading to more severe weather events.
Bluff oysters have been fished in the Foveaux Strait for over 150 years, with oysters dredged over a six-month season from March to August, after the main spawning season.
Fisheries NZ said the total allowable catch had been set at 14.95 million oysters since 1998, with commercial oyster fishers voluntarily reducing their catch to 7.5 million oysters since the 2020/21 fishing year.
In the 2023/24 fishing year, 5.9 million oysters were harvested.
Ngāi Tahu owns 20 percent of the Bluff oyster quota, and Moyle said the decision not to harvest was made earlier this year, with the aim of prioritising the long-term sustainability of the fishery.
He said two seasons ago, Ngāi Tahu harvested all but 15 percent of its quota and last season, closer to 45 percent of its total catch entitlement was left in the moana.
"We are kaitiaki of that fishery so we are wanting to ensure that it's managed well... We want to see future generations able to fish and experience Bluff oysters for many generations to come."
Oysters off the menu
Depot Eatery owner and chef Al Brown said he'd been buying oysters from Ngāi Tahu for years and he wasn't surprised when they got in touch with the news they weren't harvesting this year.
The Auckland restaurant no longer served other fish where there were concerns around declining populations, such as whitebait and tuna.
"We support our suppliers and we care about the environment and they're the kaitiaki and they play a guardianship role. It's very pivotal for them as iwi and we support that."
Brown said he wanted to serve "beautiful big fat oysters to everyone" and the restaurant would continue to serve different oysters grown in other parts of the country, including Waiheke, Coromandel and Marlborough.
"I love Bluffies as much as the next person... I believe they're the last wild oyster in the world... It's a very, very special culinary treasure and I'd hate to lose it, that's for sure."
Impacts on the Bluff oyster fishery
Fisheries New Zealand director of fisheries management Emma Taylor said last year was particularly tough for oyster fishers due to the effects of poor weather and the ongoing impacts of Bonamia exitiosa, a parasite endemic to New Zealand.
It meant catch rates were low and the quality of oysters was affected.
In order to understand how the fishery is faring, NIWA undertook annual surveys on behalf of Fisheries New Zealand to assess oyster abundance and monitor the spatial extent, prevalence, and intensity of the Bonamia disease.
She said a survey from last year showed the number legal size oysters had declined compared to previous years.
Based on that, she said catch levels were not expected to have a significant negative impact on the stock, with only around two percent of oysters taken each year.
A further survey has just been completed and preliminary results are being reviewed.
The findings would be used to inform future decisions for the fishery, with input from iwi and feedback from key stakeholders and the public.
Ngāi Tahu said it would continue to closely monitor the health and performance of the fishery and it expected to make a decision about whether to fish tio next season, by the end of the year.
