Mapping Antarctic blue whale hotspots
Scientists have identified Antarctic blue whale hotspots north of the Ross Sea and in the Mertz Glacier region, during one of the longest survey tracks for the endangered animals.
Australian Antarctic Division acousticians, Dr Brian Miller and Dr Elanor Miller, used ‘directional sonobuoys’ (underwater listening devices) to detect more than 15 000 blue whale calls between Hobart and Punta Arenas, during the second southernmost leg of the Antarctic Circumnavigation Expedition* (ACE) voyage in February.
“We’d previously detected blue whales on other research voyages in 2013 and 2015, when we entered the western edge of the Ross Sea hotspot, but it turns out that was just the tip of the iceberg,” Dr Brian Miller said.
“As we traversed north of the Ross Sea towards Punta Arenas, we continued to hear loud, intense calls and we passed more than a dozen groups within 300 km of our voyage track.”
The pair conducted ‘listening stations’ every 30 miles, recording and monitoring whale song in 12 hour shifts. By conducting stations throughout the voyage they were able to triangulate the direction and distance of loud, low-frequency calls from blue and fin whales.
“We recorded 259 hours of underwater sounds and detected blue whales on 140 of the 159 listening stations,” Dr Elanor Miller said.
“We also recorded calls from other marine mammal species including fin, sperm, killer, humpback and minke whales, as well as leopard and crabeater seals.”
As the pair were part of a broader expedition onboard the RV Akademic Treshnikov, supported by the Swiss Polar Institute, they were unable to track and sight the blue whales, as they had on previous voyages (Australian Antarctic Magazine 28: 4-5, 2015).
“We were purely listening for Antarctic blue whales to better map their distribution around Antarctica, and we’ve been able to identify hotspots in the northern Ross Sea and Mertz Glacier region,” Dr Brian Miller said.
“As we moved into the Amundsen and Bellinghausen seas, the density of calls from blue whales really thinned out.”
The pair also mapped the distribution of calls from endangered fin whales and found it correlated with that of the blue whales.
“It may be that both whale species inhabit the same areas because that’s where the krill is, but we’ll need to investigate this further on future voyages,” Dr Brian Miller said.
Two collaborating acousticians, Russell Leaper and Susannah Calderan, continued the acoustic survey on the third leg of the ACE voyage, from Punta Arenas to Cape Town. Altogether, the two teams surveyed whales on two-thirds of a circumpolar transit.
“We can use this data to compare the locations of the blue and fin whales on this voyage with historic whaling data, to see whether the mammals are inhabiting the same areas,” Dr Miller said.
“We can also use remotely sensed data from satellites, such as sea ice distribution, sea surface temperatures and phytoplankton abundance, to see if there are any relationships between the whales’ locations and environmental conditions.”
The research is part of the Australian Government’s ongoing commitment to the International Whaling Commission’s Southern Ocean Research Partnership. The partnership aims to develop, test and implement non-lethal scientific methods to estimate the abundance and distribution of whales and describe their role in the Antarctic ecosystem.
*The project 'Acoustic mapping of endangered Southern Ocean whales' was made possible via funding from the Swiss Polar Institute and Australian Antarctic Division, with in-kind contributions from Australian and international collaborators.