Numbers of endangered southern right whales continue to recover, even with slowing birth rate

The population of southern right whales in Australian waters continues to recover amid a possible slow-down in reproduction frequency, an annual survey of the species in the Great Australian Bight has found.

Typically, southern right whales ‘calve’ on a three-yearly cycle. The most recent data from the Great Australian Bight Right Whale Study suggests that rate has declined to every four to five years.

It also found fewer whales skirting the nation’s south-west coastline compared to previous assessments.

But study lead Dr Claire Charlton from Curtin University’s Centre for Marine Science and Technology says while these changes will be studied with data from future surveys to determine longer-term trends, the species’ overall trajectory remains positive. 

While fewer numbers were spotted in Bight surveys this year, numbers across the species’ coastal range from Geographe Bay south of Perth to waters off Warrnambool Bay in Victoria has increased.

“We know that whale numbers are increasing along our coastlines and our distribution range is expanding,” Charlton says.

A century overcoming the odds

In the 1920s, it was believed no more than 300 individual southern right whales existed in the southern hemisphere – an ‘extinction near-miss’ in the face of intensive whaling across the world’s oceans.

Wind the clock forward a century, and the population has enjoyed a magnitude increase to be around 3,000 in Australia alone.

But threats continue to put whales across the globe at risk, and southern rights are no exception.

Entanglement in fishing lines and nets, disturbances from ocean vessels and noise produced by underwater activity all disrupt normal whale behaviours.

Underwater noise disturbances are known to blunt the ability of marine animals to communicate, target prey and can increase stress levels. Seismic activity by fossil fuel exploration companies has also been shown to put cetaceans – a group of mammals that includes whales and dolphins – at risk, by causing behaviour modifications like panic diving.

South Africa’s courts last week provided a glimpse into the way legal protections can help safeguard marine life, when they banned Shell from undertaking off-shore oil and gas exploration.

Ironically, Australia’s southern right whales may come into greater human conflict thanks to their successful resurgence. Rather than needing to protect them from whalers, it may now be a question of legislating more reservations to avoid encounters with ocean vessels.

“We know that the key threats to these listed species are noise interference, habitat disturbance, shipping, potential ship strike and entanglement as well as prey depletion and climate variants,” says Charlton.

“This is why we need to continue to monitor and research the population annually to understand the trends in the population, their natural cycles, and the biology of the animals in order to inform the conservation management.”

Rights in the Bight a triumph of collaboration

The Great Australian Bight spans the South and West Australian coasts and is a region that southern right whales frequent to gather and calve.

It has been the subject of three decades of surveys to track numbers of right whales in the region, supported by the local Yalata Anangu Aboriginal Corporation and a range of other stakeholders. Yalata is an Aboriginal community located on South Australia’s far west coast on the traditional lands of the Wirangu people. The adjacent Mirning language group has important cultural associations with southern right whales.

These communities also have a burgeoning ecotourism industry thanks to the recovery of whale populations.

The study, now into its fourth decade, is an exemplar of productive science-community collaboration. With funding from Minderoo, researchers from Curtin University, Current Environmental and Flinders University continue surveying whales in the region, supported by Traditional Custodians, citizen scientists, local businesses and other government and non-governmental organisations.

This year, more than 100 whales were daily observed from the Head of the Bight, the northernmost bay within the region.

“The Head of the Bight had upwards of 100 whales a day inside the primary nursery grounds, which has provided phenomenal viewing for people from all over the country and the world,” says Charlton.

“We had 13 pairs at Fowler’s Bay this year – incredible tourism.

“Down in a small aggregation area of Encounter Bay [500 kilometres south west of the Bight] there’s five resident pairs, so there’s connectivity across the coast.

“It’s really important to capture the significance of this growing whale population … we’re talking about hundreds of whales along our coasts. Their distribution is expanding into new habitats.”