Scientists say a bumper season for southern right whales in South Australia is a “sign of hope” for the state amid the ongoing effects of a devastating algal bloom.

Flinders University marine biologist and chief scientist of the Australian right whale research program, Dr Claire Charlton, said research teams were pleased to record early sightings of almost 200 whales off the state’s coastline, after lower numbers in recent years. It comes amid concerns about the harmful algal bloom which has caused the deaths of some marine life off the SA coast.

“This week we recorded almost 200 whales across South Australia, with 70 females and calves at Head of Bight, nine females and calves at Fowlers Bay and four females with calves at Encounter Bay. These are record numbers observed since 2016,” Charlton said.

“We were hoping for a bumper year, and we’re really relieved that there’s a lot of whales around. It’s a good sign that they still are recovering and coming to our waters – this is a good sign of hope.”

The bumper season coincides with the 30th anniversary of the Great Australian Bight marine park, one of the primary calving grounds for southern right whales. The whales migrate from their sub-Antarctic foraging grounds to the Australian coast between May and October for calving, nursing and mating.

The long-term data showed southern right whales often returned to the same places, Charlton said. “This year, we know that there’s a female here having a calf, that she might be as old as 50 or more, and she was first sighted with a calf in 1984. We have another female here having her 12th calf sighted at Head of Bight,” she said.

“They have this imprinted memory where often the mothers will return to the same place where they were given birth to, and they’ll return to that site to calve.”

While celebrating this season’s numbers, scientists cautioned that recent research drawing on 30 years of data, published in Marine Mammal Science and the Journal of Cetacean Research and Management, showed population growth was slowing and reproductive success declining.

Southern right whales were depleted to near extinction from commercial whaling in the 19th and 20th centuries, Charlton said. It took decades after their protection in 1935 to see signs of their recovery and presence in Australian waters, and they remain listed as endangered under federal environmental laws.

Aerial survey data from 1976 to 2024 indicated the current population size ranged between 2,346 and 3,940 individuals (or 16% to 26% of pre-whaling levels), with declines in calf abundance since 2017.

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While celebrating this season’s numbers, scientists cautioned that long-term population growth was slowing and reproductive success declining. Photograph: Richard Twist

Charlton said there were concerns about marine heatwaves and the ongoing algal bloom along the SA coast, particularly given the bloom’s presence around the Fleurieu peninsula near Encounter Bay, where the whales often reside. But so far the overlap between the algal bloom and the whale’s range was limited.

“It’s certainly something that requires future research and monitoring to understand the effects, and projections and forecasts for the future,” she said.

“We do know that globally, heatwaves are affecting the foraging success and the reproductive success of baleen whales and of southern right whales.”

Marine biologist Dr Michael Bossley, who has been tracking the effects of the algal bloom, said while it didn’t appear to directly cause fatalities in marine mammals, there was a concern about the potential long-term impact on food resources for animals like dolphins and seals.

However he said that southern right whales do not feed in the waters off the South Australian coast.

Bossley said the bumper whale numbers were “excellent news”.

“At least from the whale’s perspective – that’s some good news amid the gloom.”