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How does gulp feeding work in rorqual whales?

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Illustration showing various cetaceans, including baleen whales like the blue whale, fin whale, humpback whale, gray whale, sei whale, northern right whale, and bowhead whale, as well as toothed whales such as the sperm whale, narwhal, beluga, Baird's beaked whale, killer whale, dolphins, and porpoises. Each species is labeled with its scientific name and typical or maximum length, with a size scale in the corner for reference. — cetacean Whales (order Cetacea).

Rorqual whales, which are baleen whales, utilize a specialized feeding method known as gulp feeding to capture large volumes of prey, such as krill and small fish.12

This process is made possible by the unique anatomy of the rorqual, which features ventral grooves extending from the chin and jaw down to the belly. These grooves allow the oral cavity to expand significantly during the feeding process.32

To execute a gulp, the whale opens its mouth to take in a massive quantity of water containing its prey. Once the mouth is closed, the whale uses its baleen apparatus—comb-like structures made of keratin—to strain the water out while trapping the prey inside. After the water is expelled, the whale swallows the remaining food. This method differs from skim-feeding, where whales swim through concentrations of zooplankton with their mouths open for extended periods.12