Blue whales just might be the world’s biggest and pickiest eaters! They are the largest animals on the planet yet they feed on one of the smallest. They are specialist foragers that feed exclusively on krill, small crustaceans that are found near the bottom of the marine food chain. Krill are widely distributed throughout the world’s oceans and are found in varying densities depending on environmental conditions and primary productivity. Not only do blue whales rely on a single food source but now researchers have found that they will only forage when krill densities are high enough to make lunge feeding energetically feasible.

The team from NOAA, Oregon State University and Stanford University analyzed movement data from 55 tagged whales in conjunction with prey data. The study, published last week in the journal of Science Advances, found that blue whales foraged in areas of prey patches greater than 100 krill per m3 but not below this threshold. Foraging success, as determined by the number of lunges, increased with both prey density and the number of prey patches.

Lunge feeding is an energetically costly behaviour that allows blue whales to gulp up to four tonnes of krill a day. This complex foraging strategy is energetically efficient and allows the animals to conserve energy until a prey patch is worth pursuing. This concept is believed to be the reason behind the blue whale’s enormous size and provides new insight for policies to protect this endangered species.