(Editor’s note: This report is based on a story originally published in “Inside JEB,” the online news site of the Journal of Experimental Biology. Ari Friedlaender can be reached for additional comment at (919) 672-0103 or firstname.lastname@example.org.)
DURHAM, N.C. – Highly maneuverable and built like torpedoes, minke whales are the most common whales in Antarctic waters, yet the animals could be living on a knife edge as their sea-ice habitats dwindle rapidly, according to a new study by an international team of scientists.
The scientists – from Oregon State, Duke and Stanford universities and the Australian Marine Mammal Center – published their findings online this week in the Journal of Experimental Biology.
The research, which used nonlethal, high-resolution digital tags to track the animals, is the first to show that Antarctic sea ice is an important feeding niche for minke whales.
It is also the first to observe the extreme feeding behaviors – including the fastest lunge rate ever recorded – the animals use to catch swarms of krill that live under the ice’s protective cover.
Sea ice around the Antarctic Peninsula has decreased dramatically in the last 30 years due to climate change, yet until now, scientists did not know how critical the region’s sea ice was as a habitat for the whales, says lead author Ari Friedlaender, associate professor of fisheries and wildlife at Oregon State and adjunct professor at the Duke University Marine Lab.
To conduct their study, Friedlaender and his colleagues, who are members of the Southern Ocean Research Partnership, an international group of researchers dedicated to non-lethal whale research, headed to Antarctica in 2013.
Team members included Doug Nowacek, Andy Read and Dave Johnston, all of the Duke Marine Lab, Jeremy Goldbogen of Stanford, and Nick Gates of the Australian Marine Mammal Center.
Tagging a minke whale is much trickier than tagging other whale species that inhabit the region’s icy waters, Friedlaender says, because they are smaller, faster moving and don't spend a lot of time at the surface.
Using carbon-fiber poles and suction cups, the team was able to tag two minkes who were discovered socializing in a pod of up to 40 other minke whales in the icy waters of the Antarctic Peninsula’s Wilhelmina Bay.
The digital tags, which each cost $25,000, stayed on the whales long enough to record a total of 27 hours of dive data.
Depth, acceleration, and body orientation data from the subsequently recovered tags revealed that the minkes’ feeding behavior was dramatically different from that of other whales.
“They lunge to take in prey as many as 24 times during a single dive, or over 100 times an hour – almost once every 30 seconds,” says Friedlaender. By comparison, blue whales only lunge up to four times per dive, and smaller humpback whales only lunge up to 12 times.
When the team analyzed the recorded dive patterns, they realized that the minkes were using three distinct hunting tactics.
In the first tactic, they remained near the surface and lunged to swallow mouthfuls of krill only one to two times. In the second tactic, they plummeted to depth of 100 meters and lunged about 15 times.
In the third tactic, the whales swam just below the surface, skimming the underside of the ice and gulping down krill at incredibly high rates. This tactic appears to be completely unique to minke whales, Friedlaender says. It’s particularly well-suited to hunting for gatherings of small prey under sea ice.
Having proved that it is not necessary to kill whales to understand their feeding behavior, Friedlaender and his colleagues plan to return to Antarctica next austral summer to tag more minke whales and learn more about how the animals interact with their surroundings, and how the shrinking ice cover is affecting them.
“Tagging opens up a huge window of opportunity to study the Antarctic ecosystem in a much more holistic way,” Friedlaender says.
The study was funded through a National Science Foundation Office of Polar Programs RAPID grant (#1250208) to Friedlaender.
CITATION: “Feeding Rates and Under-ice Foraging Strategies of the Smallest Lunge Filter Feeder, the Antarctic Minke Whale (Balaenoptera bonaerensis)” by A.S. Friedlaender, J.A. Goldbogen, D.P. Nowacek, A.J. Read, D. Johnston and N. Gales, published August 13, 2014, in the Journal of Experimental Biology. doi:10.1242/?jeb.111567