Abundant krill return to Upwelling

When the coastal krill Nyctiphanes australis is abundant it often swarms at or near the surface, but for a number of years we have had few sightings of krill surface swarms. This has been disappointing as abundant surface swarms are not only a sign of a productive upwelling season, but they make it easier for blue whales to find and consume their prey. In turn this makes it easier for us to find and study the whales and their behaviour. The apparent shortage of krill has coincided with a number of ‘lean’ blue whale seasons, during which the whales have been difficult to find in the vicinity of Portland, roughly the geographical centre of their upwelling feeding ground. The 2016-17 season was shaping as yet another lean season, with few sightings of blue whales reported to us, and no evidence of abundant krill.

This changed on 28 February 2017 when we flew our first aerial survey of the season, funded by Australian Geographic and the W.V Scott Estate, which covered the continental shelf between Beachport, SA and Port Fairy, VIC. We saw the first blue whale soon after leaving Portland airport, the first of 11 during the survey. While sighting 11 blue whales was rewarding but not exceptional in terms of our surveys, it soon became evident that the real story of the day was the abundance of krill. There were thousands of swarms right across the survey area but most abundant in Discovery Bay to the west of Portland. All the blue whales sighted were close to krill swarms, but only one of them was actually feeding; the others were moving very slowly, most likely well fed and in no hurry to move elsewhere.

We have long been trying to understand the dynamics of the upwelling and how it influences krill abundance – the key to understanding blue whales in the Bonney Upwelling. The 2016-17 upwelling season was unexceptional, with only weak upwelling up to the date of our survey. However, the previous (2015-16) upwelling season had been relatively strong and the abundance of krill this year may be a consequence of oceanographic conditions a year ago.

Interestingly, two days after our aerial survey the first strong, sustained upwelling event of the season commenced. Only a week before the aerial survey we had been out in our boat in the area where some of the blue whales were sighted, and had seen no sign of krill or whales. Were they somehow responding to environmental signals that heralded the belated onset of upwelling in the region?

On 10 March we returned in the boat to the area where seven blue whales were sighted during the aerial survey – and found no krill or whales! If we hadn’t done the aerial survey we could be excused for thinking that it was yet another lean year for blue whales and krill. But we know they are out there and can’t wait to get out there again.

A blue whale surfaces through a krill swarm without feeding, suggesting it was already full

A blue whale surfaces through a krill swarm without feeding, suggesting it was already full

Blue whale research season under way

The 2016-17 blue whale research season got off to a late start but is now well underway. Our core programs for this season are the Marine Science Youth Mentoring Program, our continuing blue whale photo-identification program, and our aerial survey program. This is the fourth time since 2010 we have conducted the Mentoring Program, which continues to be popular with local high schools. In essence, the schools selected four students who are joining us for four days of boat-based research on the Southern Ocean south of Portland, searching for blue whales as part of our long-term photo-ID work. They learn the basics of seamanship and boat handling, insights into the ecology of blue whales and other fauna of the Bonney Upwelling, and an introduction to marine science methods with a focus on cetacean research. Our aim is to provide a unique opportunity that will encourage local youth to consider a future in marine or environmental science in our region. The program is funded by the Isobel and David Jones Family Foundation of Warrnambool, the W.V. Scott Estate and Australian Geographic Society.

Students Braiden Malady, Jack Caithness and Caitlyn Billington search for blue whales aboard 'Bonney Blue'

Students Braiden Malady, Jack Caithness and Caitlyn Billington search for blue whales aboard ‘Bonney Blue’

The 2015-16 Blue Whale Season

This season we have had funding to carry out aerial surveys and boat-based photo-identification (photo-ID) studies, and also to upgrade our photo-ID catalogue of whales identified over the years.

We have been contracted to conduct three large-scale aerial surveys in the Great Australian Bight for the South Australian Government, two of which have been successfully carried out (as at March 2016). Funding for this and other research projects was provided to the SA Government by oil giant BP, to fill knowledge gaps in response to concerns about their plans to drill for hydrocarbons in deep water south of the Head of Bight.

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Our two surveys in December 2015 and late January 2016 found few cetaceans in the remote waters of the Bight. That is the reality of the Bight, where whale numbers (at least blue whales) are probably low much of the time, but where feeding blue whales can very occasionally be very common. Our third and final survey in this program will take place during April.

In late February we found 10 blue whales during an aerial survey of the shelf between Port Fairy VIC and Beachport SA, part of our ‘core’ study area between Cape Otway VIC and Robe SA. While this was  encouraging, it was well down on numbers found during some previous years. This survey was funded by the WV Scott Trust, and has given us a rare window into the large-scale distribution of the blue whales during the peak of the feeding season. We have funding for one more aerial survey of our ‘core’ study area, provided by the Klein Family Foundation; this survey will occur during late March.

Although It has been the most intense upwelling season for several years, blue whale numbers around Portland and surrounding areas have been disappointingly low again this year. It’s impossible to know what’s going on, as blue whales can choose from a range of alternative feeding areas such as the vast Sub-tropical Convergence to Australia’s south, and for all we know, many of them may be feeding down there. We have not yet committed ourselves to our boat-based photo-ID program until we get a better idea where to focus our effort: around Portland, or over the border in South Australian waters. In the past we have found that late March-early April is a good time to find blue whales.