There’s a lot we do not know about pygmy blue whales. But research cruises off North West Cape and more recently at Perth Canyon to tag and track the endangered animals will provide previously unknown information about where they feed along their annual migratory journey from southern Australia to northern tropical waters where they breed.
This research led by AIMS marine megafauna scientist Dr Michele Thums, sought to use satellite tags to record detailed data of the pygmy blue whales’ movement behaviour up the Western Australian coastline through the petroleum-rich North West Shelf to Indonesia.
“Pygmy blue whales have been tagged at their main known feeding aggregation in Western Australia’s Perth Canyon but these transmitted low resolution data and nearly all stopped transmitting before the whales reached North West Cape so we did not know much about their migration behaviour beyond that point, and importantly, where they fed along the way” she said.
The whales’ behaviour and their low numbers means that it is hard to find them and to study their movement patterns.
“They are usually found a long way from shore at the edge of the continental shelf, and they are quite elusive animals, spending a lot of their time underwater,” Dr Thums said.
Dr Thums and her research partners, Captains Curt Jenner AM and Micheline Jenner AM from the Centre for Whale Research (CWR), searched for the pygmy blue whales in waters as deep as 1000 metres by combining visual observation with underwater song detection.
The visual observation was from a small spotter aeroplane and from the CWR Research Vessel Whale Song.
“When the whales come to the surface to breathe, they forcefully expel air through the blowhole and the spray, known as “the blow”, is visible from the ship up to 5 miles away,” Micheline Jenner said.
Despite the visual means of observation, finding pygmy blue whales in the open ocean is not a simple task so using acoustic detection equipment was a crucial tool in their search.
“In this particular project, we dropped passive acoustic sensors, called sonobuoys, into the ocean to make initial acoustic detections from up to 100 km away,” Micheline Jenner said.
Sonobuoys have in-built hydrophones (underwater microphones) and the whale calls picked up by them are transmitted by radio signals to the RV Whale Song where acoustician Assoc. Prof. Rob McCauley, from Curtin University’s Centre for Marine Science and Technology (CMST) and Curt Jenner were able to calculate the approximate position of each calling whale.
But according to Dr Thums, even once blue whales are found it was still “very difficult” to work with them and attach the small satellite tracking devices, because they are usually underwater, spending only short periods of time at the surface.
“To tag these animals we need to come alongside them with a small boat, within around 15 m of them when they come to the surface to breathe, which is only for a few seconds, so being in the right place at the right time is very difficult, especially when sea conditions are often less than perfect,” Dr Thums said.
Despite the often-rough sea conditions the researchers attached tracking devices to six whales. These satellite tags are tiny and were designed to stay on the whales from a few weeks up to a few months before falling off, which is enough time to cross the North-West Shelf on their way to Indonesia. Half the tags are still attached and transmitting with durations of up to nine weeks so far.
The tracker receives GPS signals and transmits the GPS data to a satellite when the whale surfaces to breathe, and the whale position data is then relayed to the researcher via a processing centre.
Mr. Jenner said the “state-of-the-art” LIMPET tags (Low Impact Minimally Percutaneous Electronic Tag) collect high resolution data and were designed not to harm the whales by implanting only into the outer blubber layer of the whale.
“We can find out where these animals travel pretty much every time they surface to blow and when they dive the tags are also getting dive profile data. So, they are very useful for providing additional information to determine where the animals are feeding,” he said.
Until now this information had not been available because few whales had been tagged, the older tag technology did not last for long and the tags used did not provide GPS positions but rather Argos satellite positions only, which are not as accurate.
“Whenever the whales slow down and circle, as they do when they feed, the GPS will show us that. Whenever they do a deep dive to try and find some krill at depth we will see that as well. The diving behaviour is transmitted when they come to the surface and the satellite sends those data packets via the internet to our computers so it is quite an amazing bit of technology,” Mr. Jenner said.
The North West Shelf is Australia’s largest and most valuable petroleum production area and it is also a habitat for threatened species such as pygmy blue whales.
“This data will help us work out where the whales feed, important information for governments and industry need to reduce potential threats to these endangered whales from these and other human activities so that these areas can be protected,” Dr Thums said.
This scientific endeavour by AIMS with collaborators from CWR and Curtin University is part of the North West Shoals to Shore Research Program funded by Santos to better understand Australia’s marine environment.