Monday, December 17, 2007

For fin whales, feeding is a real drag

The word "big" doesn't do justice to whales. Humpback whales can weigh up to 40 tons. Fin whales have been known to reach 80 tons. Blue whales, the biggest animals to have ever lived, reach 160 tons - the same mass as about 2,000 grown men or 5 million grown mice.It takes a lot of food to build such giant bodies, but how exactly the biggest whales get so much has long been a mystery. "We don't have much of a sense of these animals in their natural environments," said Nick Pyenson, a biologist at UC Berkeley. For decades, whale experts had only indirect clues. "It's primarily from dead animals or from a few people standing on a ship seeing whales come to the surface," he said.With so little information, scientists have struggled to make sense of several enigmas about the biggest whales. "It's always been a mystery why they have really short dives for their body size," Pyenson said. The bigger a marine mammal is, the longer it should be able to dive for food, because it has more muscle tissue in which it can store oxygen. Other species follow this pattern, but the biggest whales do not.Pyenson and his colleagues may have solved some of the gastronomical mysteries of these leviathans by creating the first detailed biomechanical model of a feeding fin whale. In essence, they have created the world's biggest gulp.The model was made possible by a happy accident. In 2003, scientists at Scripps Institution of Oceanography in La Jolla (San Diego County) chased after fin whales and stuck small monitors to their backs with suction cups. After several hours, the monitors fell off and the scientists retrieved them. They hoped that the monitors would record fin whale songs, but they had the bad luck to encounter whales that were feeding, not singing.Jeremy A. Goldbogen, then a graduate student at Scripps, realized that the project was not a failure. Goldbogen, who is now at the University of British Columbia, was interested in how fin whales feed. The monitors had logged lots of valuable information about the movements of the whales, like their speed and depth, that he could analyze. "This is the first time we've ever seen this kind of data," Goldbogen said.Working with Robert Shadwick at the University of British Columbia and Pyenson, Goldbogen applied some basic laws of physics to the data, combining it with information about the size and shape of fin whale bodies. They ended up with a surprisingly detailed picture of what the whales do when they feed, which they recently published in the journal Marine Ecology Progress Series.It turns out that a fin whale dives very deep for food. It plunges more than 600 feet below the sea surface, most likely in search of giant swarms of krill. What the whale does next came as a complete surprise to the scientists. "It was still swimming, but it was slowing down really fast," Goldbogen said. Even as the whale pumps its powerful tail, it comes to a compete stop in three seconds.The whale grinds to a halt, the scientists concluded, by opening its mouth. Water floods in, pushing its giant lower jaws back until they hang perpendicularly from its body. Suddenly the whale is producing colossal amounts of drag. "The whales are beautifully streamlined so they can swim fast and efficiently, and then they're throwing it all out the window," Goldbogen said.In fact, a fin whale's body turns out to be exquisitely adapted for increasing its drag. The underside of its mouth is made up of a unique set of pleats that can stretch to four times their normal size. By continuing to beat its tail, the whale forces more water in, causing its mouth to expand like a parachute. And just as race car drivers use parachutes to slow them down, the whale's inflated mouth brings it to a dead stop.Goldbogen and his colleagues calculate that in just three seconds, the mouth of a 60-foot fin whale fills with more than 18,000 gallons of water. That's the same volume as a school bus, and weighs more than the whale itself.The whale then takes three seconds to shut its jaws. As its pleats begin to snap back in place, it pushes the water out of the sides of its mouth. The water must first stream through a set of thin plates known as baleen. Any krill or other animals in the water get stuck there. Once the whale has pushed out all the water from its gulp, it can swallow its prey and move forward again.If Goldbogen's model is accurate, it means that fin whales use a huge amount of energy to feed. This cost of lunge feeding, as this style of eating is known, could explain why the whales spend so little time underwater. While they can store a lot of extra oxygen in their muscle, they burn it up quickly with their peculiar way of sweeping up food.For all this effort, a bus-size gulp of water yields a fin whale only about 20 pounds of krill. But fin whales can gulp every 30 seconds. In about four hours a whale can catch a ton of krill, which provides enough energy to fuel its gigantic body for an entire day.Fin whales belong to a lineage of giant whales known as rorquals, which includes other heavyweights like blue whales and humpback whales. All rorquals share several unique traits, like the stretchy pleats on their undersides. Scientists have suspected that all rorquals feed in the same way, and new data supports that hunch. Researchers at the Cascadia Research Collective in Olympia, Wash., have been tagging blue and humpback whales with data monitors, and Goldbogen sees the same patterns of stopping and starting that he and his colleagues saw with fin whales.Now Goldbogen and his colleagues are investigating how rorquals got to be so big. Whales moved from land to sea starting about 50 million years ago, but they remained relatively small until the rorquals evolved about 7 million years ago. "They really evolved very fast," Goldbogen said. "We think this lunge feeding opened up a new door, evolutionarily speaking."To test this hypothesis, Goldbogen and Pyenson want to compare the size and shape of living and fossil whales. "When we look at all the sizes and shapes, we're going to be able to figure out exactly how lunge feeding evolved and whether it's responsible for these really big whales we see today," Goldbogen said.The scientists have been visiting museum warehouses in recent months to make measurements of whale skeletons. It can take hours - and forklifts in some cases - to gather the data on these enormous bones."I was amazed that no one has measured these things before," Goldbogen said. "But when I got there, I realized, 'Wow, this is why."' article appeared on page C - 1 of the San Francisco Chronicle

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