RARELY seen ‘courtship’ behaviour of three pygmy blue whales has been spotted in Discovery Bay.

Scientists are not 100% certain it is the prelude to mating though it is highly likely, according to the Blue Whale Study’s Dr Pete Gill.

“During a recent aerial survey we had this amazing sighting of a ‘racing group’ of three adult blue whales in Discovery Bay about 30km west of Cape Bridgewater,” he said.

“We believe the lead is an adult female and the other two are adult males.

“In Canada similar groups have been biopsied, showing that the lead animal in these trios was always a female, being trailed by two males.

“The lead animal in our sighting – presumably a female – was clearly calling the shots, powering along at 15-20 knots, with constant changes of direction, occasionally pausing for a brief rest before powering off again.

“Meanwhile, the two males battled to physically displace each other, while trying to stay close to the female, and always just below or behind her.

“We assume that this is a process of mate selection, in which the female might choose the stronger and more vigorous male as a sexual partner. We don’t know if these breeding partnerships are long-lasting or temporary, but as females only give birth every two to three years, they are probably temporary.

“Either way, it is extremely rarely seen behaviour, which we have seen only once before, in 2003. And it is perhaps the most spectacular behavioural display by any animal, combining massive size, power and grace.”

Dr Gill said the sighting was also notable for another reason: a scarcity of whales in local waters despite a remarkable Bonney Upwelling season.

“This has been an exceptionally strong and sustained upwelling season, which started in November and is now tailing off,” he said.

“We have satellite images from February, open sourced from Australia’s Integrated Marine Observing System (IMOS.  One reads the amount of chlorophyll on the ocean surface and the other is a sea surface temperature image. The chlorophyll image is particularly dramatic.”

The whales are drawn here during the upwelling season to feed on krill.

“Every year is different – sometimes krill and blue whales are abundant, in others they are scarce,” Dr Gill said.

“In some years upwelling is strong, in others it is very weak. We are still trying to understand the underlying reasons for this variability, and trying to understand the role climate change may be playing in all of this.

“In any event, this season has been one of the strongest and most sustained on record. You might think that the stronger the upwelling season, the more pygmy blue whales, but that is not always the case; in fact, this season they have been very difficult to find.

“It’s possible that the upwelling has been too strong, that the continued influx of cold upwelled water hasn’t allowed the processes of life to really take off.

“We have sighted almost no krill surface swarms this season, which is unusual, and commercial fishers have reported low catches and anomalous distribution of animals such as bluefin tuna.

“However, the other day we sighted a group of 11 pygmy blue whales feeding not far from Portland, possibly a sign that the upwelling is belatedly coming to life.”

To find the whales, Dr Gill and fellow researchers with the Blue Whale Study, carry out aerial surveys, flying along pre-determined transects to cover particular areas of interest. Since 1998 they have flown 285 aerial surveys and counting, covering ocean waters from the west coast of Tasmania and Bass Strait to the central Great Australian Bight.

“Over this time we have sighted more than 1400 pygmy blue whales from the air. We also see huge schools of dolphins, white sharks, leatherback turtles, albatross and sperm whales.”

At the end of the feeding season, the pygmy blue whales will migrate around the coastline of Western Australia to calving grounds in Indonesian waters, where they continue to feed, due to rich upwelling that occurs there during winter.

Adult pygmy blue whales average around 22 metres in length and are a subspecies of the blue whale, which is rarely seen in local waters. They range from the sub-Antarctic zone to the southern Indian Ocean and southwestern Pacific Ocean, breeding in the Indian and South Atlantic oceans, and travelling south to above the Antarctic to feed.

Blue Whale Study is a local, independent, not-for-profit research and education organisation. Dr Gill, who lives in Tyrendarra, has been studying the ecology of pygmy blue whales in their upwelling habitat in this region since 1998.

“I was fortunate to stumble onto a situation no one had previously been aware of.”