Whale trackers make rare sighting
Whale observers working for the Australian Antarctic Division hit the jackpot recently when they encountered a pod of one of the most rarely seen and least known cetaceans in the world – the Shepherd’s beaked whale (Tasmacetus shepherdi).
David Donnelly was among three whale observers working for Antarctic Division scientists studying blue whales off the coast of Portland, Victoria, when they detected a group of 12 beaked whales. He and fellow observers, Natalie Schmitt and Paul Ensor, couldn’t believe their luck.
‘We were in the midst of some long-finned pilot whales and bottlenose dolphins when we saw some unusual blows about 500 m away, which we agreed were from beaked whales,’ David says
‘As we got closer I was fairly confident they were Shepherd’s beaked whales, but we needed to be sure before we committed to an identification.’
The team made detailed observations and took still photographs and high resolution video footage of the whales as they surfaced over about 20 minutes.
‘I knew the whales were a species I hadn't seen previously and my immediate intuition was the rarely sighted Tasmacetus shepherdi due to their relatively large size, their long beak, prominent melon [forehead] and spectacular pigmentation,’ Paul says.
‘However, being somewhat conservative in species identification, I did not trust my intuition and tried immediately to think of other potential candidates.’
In the past, Shepherd’s beaked whales (which remained undiscovered until 1937) were difficult to identify because their physical appearance was primarily documented from stranded animals, whose distinctive pigmentation patterns deteriorate soon after death. At-sea and aerial sightings were, and still are rare (with only five unconfirmed sightings prior to 2006), as the animals are believed to be low in abundance and to frequent deeper, circumpolar waters, ranging from the latitudes of South Australia to the sub-Antarctic – a region little-visited by research vessels. This lack of information led to differences in the published accounts of the whales’ colour patterning. However, in 1994, fresh, stranded specimens of adults and juveniles were discovered in New Zealand, allowing scientists to accurately describe the whales’ distinctive pigmentation and to document that the pattern was constant from juvenile to adult.
‘Shepherd’s beaked whales have a distinctive head shape and a pigmentation pattern which is perhaps the most diagnostic of all the beaked whales,’ Paul says.
‘The overall body colouration is brownish-grey, the beak is dark, the melon is lighter in colour as far back as the blow hole, there is a dark eye-patch and a dramatic extension of light colouration which extends diagonally onto the flanks up from just behind the flippers. There is also a lighter colour extending onto the flanks behind the dorsal fin.’
David, Paul and Natalie say their documentation of this unique sighting will add greatly to what cetacean biologists know about Shepherd’s beaked whales, with good descriptions of their physical appearance, pod composition and surfacing behaviour.
‘Our sighting will validate and increase the knowledge of pigmentation patterns and will be useful for updated cetacean field guides and to facilitate at-sea identification in the future,’ Paul says.
Listening to the blues
The sighting was just one of many exciting encounters with whales that the team experienced during the three-week voyage. These encounters included a Cuvier’s beaked whale, sei whale, killer whale, sperm whales and more than 40 blue whales – the focus of the voyage.
Blue whales found off the coast of Victoria grow to a massive 24 m in length but are smaller than the blue whales found in Antarctica, which can be up to 31 m long. Because blue whales sing, they are potentially trackable using acoustic equipment that can detect and transmit their low frequency calls.
Led by the Australian Antarctic Division’s Dr Mike Double, the team of observers, along with acousticians and cetacean scientists, aimed to test the ability of ‘directional sonobuoys’ – used by the Navy to detect submarines – to locate and track singing blue whales.
‘We wanted to answer questions such as how far away can we detect whales using the sonobuoys, how far away can the vessel pick up the VHF signal from the sonobuoys, do whales sing long enough for us to find them, and can we track the whales at night?’ Mike says.If the sonobuoys prove effective at locating and tracking blue whales in Victorian waters, the technology and methodology will be used on blue whales in Antarctic waters next year for the Antarctic Blue Whale Project. This flagship project of the Southern Ocean Research Partnership aims to estimate the abundance of blue whales in the Southern Ocean, 50 years after whalers killed some 350 000 individuals, as well as examine their distribution, population structure and migration routes.
Mike says the blue whale project in Victorian waters is an important step in devising a way to maximise the chances of encountering Antarctic blue whales in the vast Southern Ocean.
‘Previous methods of estimating blue whale abundance by sightings surveys from ships, allowed us to visually detect a whale from up to 10 km away in good weather, but acoustic methods can allow you to detect them perhaps as much as several hundred kilometres away, and in rough weather,’ he says.
‘Blue whale sightings from ships in Antarctica are infrequent, but if the sonobuoys allow us to get an accurate bearing on the whales from, say, 100 km away, we can steam to their location and save enormous amounts of searching effort.’
In the first of two three-week voyages (the next one will start on 12 March), the sonobuoys were deployed as needed in a 500 km study area south of Portland, Victoria. Australian Antarctic Division acoustician, Dr Brian Miller, said the first 10 sonobuoys detected nothing but ship and wave noise, as they traversed an area apparently devoid of blue whales but it was not long before the ship moved to another region and finally struck gold.
‘We heard our first blue whale singing at 2am and tracked the ship towards the sound through to 6am, when the whale stopped singing,’ Brian says.
The team estimated that the ship had approached the singing whale to within about two kilometres. At day-break the observer team then visually detected the animal and directed the ship to approach the whale during several surfacing bouts, before it surfaced some 50 m from the vessel, allowing them to take photographs for individual identification.
The team continued this process of deploying sonobuoys to triangulate bearings and get within range of whales to make visual sightings, with good success.
‘This voyage has given us confidence that sonobuoys will help us to find rare whales in Antarctica,’ Mike says.
‘During our next voyage we’ll formally test how much acoustics improves the sighting rate. Ultimately, this will allow us to calculate how much ship time is required to use the technique to estimate the abundance of Antarctic blue whales.’