One overcast morning in Antarctica, scientists caught a lucky break when they were able to cruise their small boat right into a group of about 40 minke whales. Working quickly, they attached data-gathering tags to as many of the normally elusive animals as they could—something no one had ever done before. Now, a year and a half later, data from the auspicious encounter show that minke whales have staked out a unique ecological niche that no other baleen whale can take advantage of: hunting krill under sea ice.
With the sleek silhouette of a torpedo and measuring about 6 meters long, minkes are the smallest of the baleen whales. Normally, Antarctic minkes travel solo or in small groups, keeping well away from people and not lingering at the surface. Consequently, little is known about them, despite their being the most common whale in Antarctica and the objects of Japan’s controversial scientific whaling program.
On the day the scientists cruised into the group, though, the minkes let them get close enough to attach data-gathering tags to their bodies. The team high-fived and hugged when they stuck the first tag onto one of the whales and “just went crazy” when it was still attached to its host’s back after a nerve-wracking dive beneath an ice floe, says Ari Friedlaender, a marine mammal ecologist at Oregon State University’s Marine Mammal Institute in Newport, who led the team.
Friedlaender’s team managed to tag nine minkes that day and several more over the next few days. Most of the whales carried satellite transmitter tags that gathered location data, but two carried special tags suction-cupped to their skin that recorded pressure, temperature, acceleration, and magnetic field. Together, the suction-cup tags gathered 26 hours of data, including 650 dives and nearly 3000 feeding events.
The tag data showed that the minkes did most of their feeding under the sea ice, often skimming just below the frozen water while rapidly snapping up krill swarms—a feeding style seen in no other whale, Friedlaender and his colleagues report online today in The Journal of Experimental Biology. Bigger, less maneuverable whales just can’t do that. Eighteen-meter-long humpbacks, for instance, are Antarctica’s other abundant baleen whales, but they stick to feeding in the open water and the edges of the sea ice. Dining separately may be what lets the two species coexist in Antarctica, Friedlaender says. But as Antarctic sea ice melts, minkes may find themselves with a smaller niche and suddenly competing for food with their larger cousins, spelling trouble for the species.
The tagged minkes also gulped down a remarkable number of mouthfuls of krill per dive compared with other baleen whales, which all catch prey using a behavior known as lunge feeding. The minkes lunged up to 24 times during a single dive, nearly once every 30 seconds. By contrast, blue whales, the largest baleen whales, can lunge only a few times during a dive because they gulp down much larger mouthfuls relative to their body size, resulting in immense drag. “Minke whales feed in [an] extreme manner relative to all other baleen whales,” Friedlaender says.
The new information is “a big piece of the puzzle that was missing” and it neatly confirms scientists’ predictions about how lunge feeding scales with baleen whale body size, says Robert Shadwick, a comparative physiologist who studies whales’ feeding mechanisms at the University of British Columbia, Vancouver, in Canada, and was not involved in the research. Before this study, scientists had good data on lunge feeding in large and medium, but not small, baleen whales. Shadwick adds that simply attaching recording devices to the fast, maneuverable minkes under harsh Antarctic conditions is a feat in its own right that opens new research possibilities.
Friedlaender says his research casts doubt on Japan’s scientific whaling program, which has purported to study minke feeding biology and has killed between 240 and 860 of the animals every year since 1988. “We learned more in 2 weeks of studying these animals in the Antarctic than the Japanese have ever produced,” Friedlander says. “There are ways to study these animals and their feeding behavior without taking them out of the picture.”
The International Court of Justice halted the minke hunt in March, saying it was not structured to meet its stated scientific goals. However, the Japanese are reportedly revamping their program to resume hunting later this year.