Hunting in the southwest Atlantic ocean drove whale populations to the brink of extinction, but a new study by international scientists suggests some populations may be close to a full recovery.
The survey was carried out in South Georgia Island in the south west Atlantic Ocean.
University of Auckland whale researcher Dr Emma Carroll co-led the survey and said the latest data showed protection of whales had worked.
"South Georgia has a similar latitude to New Zealand's own sub-Antarctic islands and as with our own populations of southern right whale near the sub-Antarctic Auckland Islands, we knew populations were increasing but these latest results are fantastic."
"It's also particularly significant because whales were slaughtered in their tens of thousands at South Georgia and to see them return in such numbers is just an absolute thrill."
Humpback whales were also sighted in the waters with 790 seen in just 21 days.
It was estimated more than 20,000 were feeding there in the summer months and then migrating to colder waters in the sub-Antarctic to breed.
The rare and critically endangered blue whale, the largest animal that has ever lived, was sighted just once during the first year of the survey, in 2018.
This year blue whales were sighted 55 times.
Dr Jen Jackson from the British Antarctic Survey, who also co-led the study, said "continued protection and monitoring is required to see if this unprecedented number of blue whales sightings is a long-term trend, as we see in humpbacks".
The southern right whale was not seen in 2019 although it was regularly sighted in 2018 and 2020.
Dr Jackson said that may be because they preferred to feed elsewhere in 2019, but scientists will further analyse the data to better understand feeding behaviour.
Genetic monitoring work pioneered in New Zealand's southern right whales, Tohorā, will also be used to understand how southern right whales feeding around South Georgia are connected to wintering grounds around South America.
"What is clear is that protection from whaling has worked with densities of humpbacks in particular similar to those of a century ago and we are thrilled to see them at South Georgia again," Dr Jackson said.