by Veronika Meduna
A team of New Zealand and Australian scientists has picked up the first song of blue whales this week, as their research vessel Tangaroa has reached the northern limit of the Southern Ocean.
The team is one week into a six-week voyage to Antarctica with the main goal to learn more about the top predators in the Southern Ocean, including blue whales, humpback whales and toothfish. Along the way, the scientists are also collecting continuous measurements in the ocean and the atmosphere.
‘When ever you put gear in the water or you make measurements in the Southern Ocean, you’re going to see something new.’ _Richard O’Driscoll, NIWA scientist
Richard O’Driscoll, a fisheries scientist with the National Institute for Water and Atmosphere and one of the voyage leaders, says the team will make its first stop at the Balleny islands to study factors influencing the abundance and distribution of humpback whales. This ice-covered 160km island chain in the northern Ross Sea is a known foraging area for humpbacks.
“But we don’t even know what they eat down there. We don’t know whether they are eating mainly krill or small fish called silverfish, so we’re going to do some work around counting the whales and also some trawling to work out what they are feeding on down there.”
The next part of the voyage will focus on Antarctic blue whales – the world’s largest animals, and one of the most elusive. Blue whales were hunted to near extinction by industrial whalers, and Mike Double, a science leader with the Australian Antarctic Division (AAD), says there may be fewer than 2000 of them left today. The highest densities are found near the edge of the Antarctic sea ice during summer and the team is using acoustic monitoring devices to detect the whales’ low-frequency song.
Blue whales sing at such low frequencies that their call has to be sped up eight times to make it audible to the human ear, as in this video, recorded and processed by AAD acoustician Brian Miller.
The team has already tuned in to the first calling whales this week, from a distance well south of their current position, and will be using multiple sonar buoys to pinpoint their position so that the Tangaroa can move in closer. “With the listening technology we can determine their position, move the ship to the whales, photograph them and identify individuals, take biopsies, and possibly deploy satellite tags as well.”
Two Antarctic blue whales have already been tagged during an earlier voyage two years ago, which has also identified seven hotspots where blue whales aggregate, using the same directional underwater acoustic technology. However, the tags didn't last long enough to track the whales' migration to calving grounds in warmer waters.
This survey is part of the International Whaling Commission's 10-year Southern Ocean Research Partnership project to work out how many blue whales there are and how well they may be recovering from intensive commercial whaling. “They are very long lived animals and breed slowly,” says Mike Double. “In the Southern Ocean, we think the carrying capacity is around a quarter of a million (250,000) blue whales. That’s what it was in the early 1900s, but from then to 1960 [commercial whalers] killed about 360,000 blue whales and they got down to just a few hundred individuals left. That’s what they are recovering from now.”
After the blue whale research, the Tangaroa will head further south to the Ross Sea to one of the main toothfish fishing areas, where fishing vessels from a range of countries, including New Zealand, have been catching a quota of 3000 tonnes of toothfish since the mid-1990s.
Richard O’Driscoll says the focus will be on two associated species, grenadiers and icefish, which are major prey for toothfish but are also caught as bycatch in longline fisheries. “We will look at the abundance and distribution of these species to help evaluate the ecosystem effect of the toothfish fishery in that area.”
The last objective of the voyage is to put an echo sounder mooring in at Terra Nova Bay to study Antarctic silverfish spawning over winter. “Silverfish are an important prey species in the Ross Sea. In spring, when the ice clears, we see eggs and larvae in this area, but we don’t know whether the adults swim in there and spawn during winter when it is covered in ice, or whether the larvae just drift in.”
Throughout the voyage the team will be taking continuous measurements, including gases and particles in the atmosphere, the height of clouds and plankton productivity.
'The Southern Ocean is one of the least studied environments on Earth, so most of the stuff we do and see will be new and most of it will add to the existing data sets and improve our knowledge. From the whales right down to the plankton, and the particles in the atmosphere – all the measurements will be novel and they’ll add to what we already know.'
You can follow the expedition on the voyage blog, and you can listen to our radio feature below.