The Hector’s dolphin — a species classed as nationally vulnerable — was killed in the small Te Waewae Bay Marine Mammal Sanctuary last year.
The Environmental Law Initiative (ELI) uncovered the dolphin’s death along with records of 145 other dolphin and seal deaths that happened in other marine mammal sanctuaries across New Zealand during the years 2024-25 and 2023-24.
The deaths were attributed by the Ministry of Primary Industries to commercial trawling and set-netting and also included 17 Dusky dolphins killed at Kaikoura Whale Sanctuary and 16 Hector’s dolphins killed at the Banks Peninsula Marine Mammal Sanctuary.
Some of the Hector’s dolphins killed in reserves around New Zealand were heavily pregnant female dolphins with unborn female calves, the organisation Māui and Hector’s Dolphin Defenders said.
ELI senior legal researcher Megan Cornforth-Camden said "many people assume marine mammals would be safe in marine mammal sanctuaries, yet devastatingly, that is not the case".
ELI wrote last month to Minister of Conservation Tama Potaka demanding action to stop the deaths through tougher regulatory action using the Marine Mammals Protection Act (MMPA).
In a response dated April 15 and seen by the Otago Daily Times, Mr Potaka said he could initiate a process to review and amend the rules of any sanctuary "should evidence show that [they] are not meeting the purpose for which they were created".
The minister said officials from the Department of Conservation and Fisheries New Zealand monitored bycatch against species’ threat management plans, including the Hector’s dolphin plan and if bycatch was negatively impacting populations "the Minister for Oceans and Fisheries and I will receive advice and determine whether to review protection measures".
However, ELI’s Ms Cornforth-Camden said the purpose of the MMPA was to protect all marine mammals, irrespective of threat status or weighted against fishing interests.
"Allowing ongoing fishing that kills protected dolphins and seals is inconsistent with the purpose of the law, let alone the very basic notion that these areas [where the deaths happened] are a sanctuary," Ms Cornforth-Camden said.
"If there is any hope to draw from this situation, it is that Mr Potaka has considerable legal authority to take action."
New Zealand’s reporting to the Convention on Biological Diversity said only 0.45% of the nation’s ocean is highly protected and 19.92% had other forms of protection.
World Wildlife Fund New Zealand, Māui, Hector’s Dolphin Defenders and the Endangered Species Foundation have launched a public letter-writing campaign urging Mr Potaka and MPs to strengthen marine mammal sanctuary protection.
The Endangered Species Foundation general manager Natalie Jessup said 146 marine mammal deaths in the last two years was "an absolute horror show and indefensible by any reckoning".
Environment Southland councillor Roger Hodson said the death was a "very unfortunate and avoidable outcome that highlights concerns about the compatibility of a trawl fishery operating in a marine mammal reserve".
Rakiura Marine Guardians chairman Bill Watt said "we have a lot of species in trouble or on the point of extinction and we are going be much the poorer if we cannot do what needs to be done to make populations viable".
