Matariki, the southern right whale that visited the capital last year, has helped contribute to a lower official risk status for the species.
The Department of Conservation's marine mammal conservation report released today, the first since 2013, has classified the ocean giant as at risk of extinction but recovering.
The species was previously considered threatened and vulnerable.
DOC marine mammal biologist Dave Lundquist said the tohorā's (southern right whale) genuine improvement in population was "amazing."
"We're starting to see them in places where we historically would have but not in our lifetimes," he said.
Just five New Zealand marine mammals are not at risk of extinction, according to the report.
The marine mammals classed as critically threatened are the Bryde's whale,Māui dolphin, southern elephant seal and orca whale.
"It also paints a picture of these species being really vulnerable and so we have to do everything we can to reduce the threats," Conservation Minister Eugenie Sage said.
A review of the threat management plan for Hector's and Māui dolphins will be released for public consultation before the end of July.
Of the 57 animals in the report, 30 do not have a risk classification as there is not enough known about them.
The report states this is a concern and that it's likely many of these whales and dolphins are threatened.
Mr Lundquist said the reason the 'data deficient' group has dramatically increased from the 2013 report is because the classifying panel took a stricter approach to data interpretation.
"I don't think it's a question of whether we can do more research in this area or not... it will take a collective effort by a whole range of organisations," he said.
A slow in the decline of the New Zealand sea lion, or rāpoka, has seen the species downgraded from being critically threatened to vulnerable.
Improved data on populations has led to the Hector's dolphin moving from endangered to the slightly less at-risk status of vulnerable, and the false killer whale changing from not being at risk of extinction to being assessed as at risk and naturally uncommon.
A four year campaign to get the leopard seal reclassified as a resident of the country, rather than a vagrant visitor from Antarctica, has been successful with the report reflecting the change.
NIWA cetacean biologist Krista Hupman was tasked with dealing with a leopard seal found in a marina, now known as 'Owha,' when she began researching the species presence in New Zealand.
"We're so happy... With citizen scientists, we're actually able to collect a whole heap of information that would have been missed," she said.
Ms Hupman said she wanted to thank members of the public who had led to the reassessment, which she said would increase awareness and conservation of leopard seals.
"If they are in a human environment we have to work about living along side them, rather than just removing them."
Ms Hupman said it is important an animal's classification is accurate and said she would continue to analyse public sightings called in to the 0800 LEOPARD hotline.