How do giant, toothless baleen whales filter out thousands of pounds of tiny shrimp after swallowing seawater?
Cal State Fullerton postdoctoral researcher Shirel Kahane-Rapport delves into the biomechanics of these filter feeders and how they use baleen to filter food, such as zooplankton and small fish, from seawater. Answers might lead to better designed industrial filtration systems.
Kahane-Rapport is conducting her study under the mentorship of Misty Paig-Tran, associate professor of biological sciences. Paig-Tran’s FABB (Functional Anatomy, Biomechanics and Biomaterials) Laboratory uses a blend of anatomy and engineering techniques to answer biological questions about the performance of marine animals.
“Baleen whales are fascinating. But it’s amazing how little we know about some of the biggest and most charismatic animals on the planet,” Paig-Tran said. “Studying how large animals filter tiny organisms gives us great insight into building better and more efficient filters for human use.”
Lead researcher Kahane-Rapport is conducting the study in collaboration with researchers at Stanford University, where she received her doctorate in June 2021, and the University of Washington.
Their research aims to define how body size affects the biomechanics and anatomical structures involved in water flow and prey capture in five species of rorquals, a family of baleen whales. This particular family of whales includes the blue whale (the largest of all whales and the largest animal of all time), the fin whale, the humpback whale, the gray whale and the minke whale.
In early July, Kahane-Rapport presented her research at the international conference of the Society for Experimental Biology in Montpellier, France. In August, she will present at the Society of Marine Mammalogy conference in Palm Beach, Florida.
She recently received a postdoctoral fellowship in biology from the National Science Foundation to continue her research at CSUF for the next two years. His research also includes collaboration with Paig-Tran on the biomechanics of other large filter-feeding animals such as manta rays.
Filter-feeding whales
Baleen whales have keratinous mouth tissue — the same protein as a human’s fingernail and hair — that hangs down from the roof of the whale’s mouth in bilaterally symmetrical supports, Kahane-Rapport explained. The larger patches of keratin are positioned near the lip and the smaller patches are closer to the tongue. When the whale swallows huge amounts of seawater, the hair-like baleen filters or filters food from the water.
“The edges of the baleen patch fray into hairs, or fringes, which interlock, creating a dense mat. This mat allows the huge amount of engulfed water to flow out of the mouth and enlarged throat, and retain captured prey,” added Kahane-Rapport, whose doctoral studies focused on large filter-feeding whales. . “We don’t understand the mechanics of this process.”
His study, which was submitted for publication in a peer-reviewed scientific journal, looked at different characteristics of baleen, such as the thickness, length and size of the keratin plates, as well as the spaces between each plate.
“We found that these characteristics that we measured were very different between species. This is something you would expect because they are different species, but our study shows it with statistical evidence,” she said.
For researchers, one of the most complicated aspects of studying baleen whale filtration is understanding how water passes through the filter.
“When you study a filter, you first calculate the size of the hole – known as the pore – that water passes through. Then you can determine the volume and speed of water flow through the filter” , she explained.
“In the case of baleen whales, the filter is a mat of tangled hairs that emerge from the baleen. This mat has no pattern, structure, or clear pores, so the researchers were unable to calculate the volume and velocity of this filter.
Improved artificial filters
For their study, the researchers generated CT scans of the pile carpet. Using specialized CT software and an equation more often used by industrial filter engineers, they were then able to calculate all the small spaces that appear between the hairs and add them up to create an approximate cumulative pore size. .
“We found that larger whales – blue whales and fin whales – had smaller pore sizes than smaller whales, such as humpback whales,” Kahane-Rapport said. “As a result, our research could lead to the design of a filter that can be used to improve current man-made filtration systems, inspired by the massive amounts of water efficiently filtered and treated by these giant species.”
This study also allows scientists to better understand the feeding mechanisms of these ecologically important animals. Additionally, their work focuses on the risks whales face from human-made threats, such as pollutants in the water, including microplastics.
“Baleen whales are ecologically important animals, and by understanding them better, we can improve not only ocean life, but human life as well.”