Have you ever wondered how much food it must take to maintain the body weight of a whale? For decades scientists have tried to find out how blue whales manage to take in enough food, but the massive mammals remained shrouded in mystery. According to a report from CBC, however, a new study has shown that blue whales actually have a foolproof strategy for finding food in the open ocean.

Off the coast of California, researchers used tags to trace the movements of blue whales as they chased their favorite prey, tiny crustaceans that look like shrimp, called krill. Researchers previously believed that the blue whale was a grazer, swimming through the ocean and filtering water through their baleen, a structure in their gums that traps tiny food animals but allows water to pass through.

Now, scientists are realizing that blue whales are not so carefree as they once believed. According to Elliot Hazen, a research ecologist at the U.S. National Oceanic and Atmospheric Administration’s Fisheries Science Center at the University of California Santa Cruz, blue whales actually employ a complex strategy to make the most of the nutrients available at any given time by considering a wide range of different factors.

When there isn’t a lot of prey available, researchers found that blue whales tended to conserve oxygen by relaxing their hunting efforts. When krill was abundant, researchers noticed that the blue whales kicked up the intensity of the hunt, making little effort to conserve oxygen and focusing on eating as much as possible.

The study showed that whales play a much more active role in choosing what to eat and when to eat it than researchers previously thought. The study tracked over 50 individual blue whales with tags attached to their skin by a suction cup.

Blue whales don’t face prey that is any lager than a quarter, filtering krill from the water simply by swimming through a school with an open mouth. To help them eat the krill, they push mouthfuls of water through their baleens with their tongues, leaving a large bite of food remaining inside.