NEWPORT, Ore. - Scientists for the first time have used tags to track the behavior of Antarctic minke whales and discovered that this smallest of the lunge-feeding whales utilizes the sea ice more than expected and feeds in ways unique from other species.
The study is also important from another standpoint: The researchers were able to acquire significant data on minke whales using non-lethal methods.
Minkes have been the subject of lethal sampling by some countries under the label of "scientific whaling."
Results of the study, which was funded by the National Science Foundation, are being published in the Journal of Experiment Biology.
"We know a lot about the feeding and diving behavior of larger whales, but not as much has been known about minke whales - especially in Antarctica," said Ari Friedlaender, a principal investigator with the Marine Mammal Institute at Oregon State University and lead author on the study. "They are major krill predators and understanding how and where they feed is important.
"It gives us a better understanding of how changes in sea ice might affect these whales and the Antarctic ecosystem," he added.
In their study, the researchers used suction cup tags equipped with multiple sensors to track the feeding performance of minke whales in Antarctica. They recorded 2,831 feeding events during 649 foraging dives from the tag records.
They discovered that the small size of the minke whales provides them with better maneuverability, which enables them to navigate in and around the ice to locate krill.
Unlike larger whales, however, minke whales are limited by their comparatively small feeding apparatus. In other words, they cannot take in as much krill-filled water as their larger counterparts. Larger baleen whales feed by taking a small number of very large gulps - encompassing from 100 to 150 percent of their body mass.
Minke whales, in contrast, take high numbers of much smaller gulps - no more than 70 percent of their body mass, and often much less, according to Friedlander, an associate professor in the Department of Fisheries and Wildlife who works out of OSU's Hatfield Marine Science Center in Newport, Ore.
"They compensate by making many more lunges per dive than other whales," Friedlaender noted. "They are able to do this because their physiology keeps the energy cost of each lunge very low. We documented minke whales that made foraging dives beneath sea ice that included as many as 24 lunges for krill on each dive - the highest feeding rate for any lunge-feeding whale."
The Antarctic minke whales occupy a unique niche in the ecosystem, the researchers pointed out. Penguins and seals also feed on krill, but the filter-feeding ability of minke whales allows them to consume greater quantities of the small crustaceans during their dives. The key, researchers say, is their ability to utilize dense patches of prey, which the minke whales can do because of their maneuverability.
The average dive of a minke whale was about 18 meters deep and lasted about a minute-and-a-half. However, the researchers documented dives as deep as 105 meters and lasting as long as seven minutes.
"These kinds of data are important to document because we just haven't known much about minke whales in any region, but particularly in Antarctica," Friedlaender pointed out. "The logistics of working in a remote environment, in and around the sea ice - and the difficulty of even approaching the whales - has made them a tough species to study.
"The recent advancement of multi-sensor tag technology helped make this possible."
Other authors on the paper include Jeremy Goldbogen, Stanford University; Doug Nowacek, Andrew Read and David Johnston, Duke University; and Nick Gales, Australian Antarctic Division.