Blue whale calf numbers rise after slow migration start along WA's south west coast

Researchers are beginning to breathe a sigh of relief as a late run of mother and calf blue whales looks set to equal or possibly surpass numbers recorded off Western Australia's south west coast in previous years.

Teams of spotters from two organisations positioned at vantage points along the shoreline of Cape Naturaliste, 250 kilometres south of Perth, monitor populations of various whale species from October as they migrate to southern feeding grounds.

Geographe Marine Research chair Capri Jolliffe said just three mother and baby blue whale pairings, referred to as cow and calf, had been sighted by mid-November.

"We would typically start to see numbers of cows and calves peaking by that time," Dr Jolliffe said.

"We were pretty worried."

Though all sightings are yet to be verified, 13 cow-calf pairings had been recorded by the beginning of December, which is typically the tail end of the WA leg of their southern migration.

"We would typically see around nine to 10 [pairs] in a season," Dr Jolliffe said.

The pairings are included in the 260 blue whale sightings observed off Dunsborough, while Dr Jolliffe said "thousands" of humpbacks were also recorded.

Environmental and random 'X' factors at play

While populations of humpback and southern right whales have largely rebounded after the end of commercial whaling in 1978, blue whales have been slower.

Dr Jolliffe cited successive La Nina weather events, increased marine traffic and subsea exploration as a potential impact on reproductive rates for blue whales, evidenced by sightings of the species displaying lower than normal stores of fat, or body condition.

"Given those factors, it wouldn't have been surprising to have a low year for calves," Dr Jolliffe said.

"But to have only had three would have been alarming, so it was pleasing to see that number grow."

Push for sustainable tourism

Western Australian researchers will share notes from this year's migration with colleagues in Timor-Leste where pods of blue whales also amass.

Researchers posit pods migrate south through the Banda and Timor seas from June.

Professor Karen Edyvane first photographed a mother and calf blue whale pairing off the coast of Timor-Leste in 2016 and has led research in the area since.

"This is a species which really needs what we call 'trans-boundary management,' to ensure that we get good information and effective conservation and protective measures as well," Dr Edyvane said.

"They have simply not recovered from the devastating impacts of commercial whaling, which knocked the population down to less than 1 per cent."

Dr Edyvane said a key area of concern for researchers in Timor-Leste was the impact of some whale watching operators, who did not face the same regulations as operators in Australia.

"Every year we see an increasing level of concerning and disruptive behaviour from some operators," she said.

"We are seeing mothers and calves being separated by boats, animals are being pursued for hours."

Dr Edyvane said Australia had set the "gold standard" for responsible tourism methods.

"It has some of the best and most regulated whale tourism in the world," she said.

"There is a lot of opportunity for Australia to help Timor-Leste in conserving its whales through responsible tourism."