Tag team track whale feeding habits

Dr Nick Gales successfully tags a minke whale from the bow of the inflatable rubber boat
Dr Nick Gales successfully tags a minke whale from the bow of the inflatable rubber boat. From a distance of 5-8 metres, he aims for a point on the whale’s dorsal (upper) side. The tag must stick out of the water when the whale breaches the surface in order to transmit its signal to a satellite. (Photo: John Durban)
An acoustic suction cup tag is attached to a minke whaleA pod of minkes, including one recently tagged with a green acoustic tag, in their feeding grounds in the Gerlache StraitA humpback whale carrying a satellite tagThe Australian-American tagging team dressed in red immersion suits in a small boat

Antarctic scientists have deployed data-logging and satellite tags on Antarctic minke whales to learn more about where and how the animals feed.

Australian Antarctic Division Chief Scientist, Dr Nick Gales, and colleagues from the United States Antarctic Program, successfully deployed the tags on 15 minke whales during a two-week voyage to the Gerlache Strait off the Antarctic Peninsula. The team also deployed 26 tags on humpback whales.

The data collected by the tags will provide the first insights into the diving and feeding difference between the two whale species.

‘In the Southern Ocean, most whale populations were hunted almost to extinction,’ Dr Gales said.

‘As these heavily hunted whale species recover, along with other Southern Ocean predators such as Antarctic fur seals, there is a great deal of interest in understanding how and where each predator feeds on their common prey – Antarctic krill. We know a little about this from ship-based surveys, where we have observed the range of habitats we see the different species in, but we know almost nothing of the movements of individual animals and what happens when they go below the water surface to feed.’

The United States-led voyage in February aimed to address this information gap by tagging minke and humpback whales foraging in a shared feeding ground.

Short-term data-logging tags, attached by suction cups, remained on the whales for up to 24 hours and collected comprehensive data on their movement through a krill swarm, including dive depth, fluke strokes, acceleration, and the pitch and roll of their bodies. At the same time, scientists onboard the United States National Science Foundation research vessel, Point Sur, monitored the krill swarm size and location using scientific echo sounders.

‘With software we can reconstruct the movement of the whale in three dimensions and see where and how the animal is feeding,’ Dr Gales said.

‘When we deploy this type of tag we also use echo sounders on our boat to see where the whales’ prey is located. We integrate the whale tag data with the echo sounder data to get fine resolution pictures of the whale, its behaviour and its immediate environment, including the prey.’

A second, long duration satellite tag was fired into the blubber of the animals, where it is hoped it will remain for several months.

‘The satellite tags provide us with information about the medium to large scale movements of the whales; so how they move around their feeding grounds to search for prey, where they go when they leave the feeding grounds, and we hope the tags last long enough to tell us where the whales go for their winter breeding,’ Dr Gales said.

The team used different approaches to tag the minke and humpback whales.

‘Minke whales are much smaller and faster than humpback whales,’ Dr Gales said.

‘We soon worked out that we just had to behave like a minke whale. So we slowly manoeuvred into a group of whales and when one surfaced at the right distance, I was able to fire a tag into the blubber from the bow of the boat.

‘Humpback whales, on the other hand, tend to sleep at the surface after they’ve been feeding, so we were able to drift alongside them and tag them quite easily.’

As well as providing foraging information, the research on minke whales will contribute to abundance estimates.

‘We’ve been trying to estimate the population size of minke whales for decades and they’re hard to count because they spend an unknown amount of time underwater and in and under the pack ice,’ Dr Gales said.

‘Data from the tags we deployed this summer will provide measures of the amount of time minke whales spend at the surface and the amount of time they spend in ice and open water habitats. These data will contribute to sophisticated statistical models that are used to derive the abundance estimates.’

The work is contributing directly to the Southern Ocean Research Partnership, a collaborative consortium for non-lethal whale research at the International Whaling Commission. The results from the voyage will be reported to the International Whaling Commission’s Scientific Committee in Korea in June.

Wendy Pyper
Australian Antarctic Division