Whales, diverse marine mammals inhabiting Earth’s oceans, display a remarkable array of feeding behaviors. While some hunt large prey, others consume vast quantities of smaller organisms. For certain whales, particularly the largest species, tiny, shrimp-like crustaceans known as krill form a significant portion of their diet.
The Whales That Hunt Krill
Whales are categorized into two suborders: toothed whales (Odontoceti) and baleen whales (Mysticeti). Toothed whales, like dolphins and sperm whales, actively hunt individual prey such as fish and squid. Baleen whales lack teeth; instead, they are equipped with specialized filter-feeding structures in their mouths.
The whales that primarily consume krill belong to the baleen whale group. This includes species such as blue, fin, humpback, minke, and sei whales. While their diets can also include other small crustaceans like copepods or small schooling fish, krill is a major food source for these massive filter feeders.
The Mechanics of Krill Consumption
Baleen whales employ a filter-feeding mechanism using baleen plates, which hang from their upper jaws. These plates are made of keratin, the same protein found in human hair and fingernails, and have fine, bristly fringes. The arrangement creates a sieve-like mat, allowing whales to strain tiny organisms from large volumes of water.
Different baleen whale species use varied strategies to capture krill. Rorqual whales, such as blue, fin, and humpback whales, are “gulp feeders.” They accelerate towards dense krill patches, opening their mouths wide to engulf enormous quantities of water and prey, sometimes nearly doubling their body weight in a single gulp. The whale then forces water out through the baleen plates, trapping the krill inside to be swallowed.
Another feeding method is “skim feeding,” practiced by right whales and some sei whales. These whales swim slowly with their mouths open, allowing krill-rich water to flow in. The baleen plates filter the food as water exits. Gray whales are bottom feeders that suck in sediment from the seabed and filter out invertebrates, including some crustaceans, using their coarser baleen.
Krill’s Role in Whale Diets
Krill’s abundance in specific ocean regions, particularly the Southern Ocean, makes it an accessible and concentrated food source for baleen whales. These tiny crustaceans often form vast swarms, allowing whales to consume large amounts of prey efficiently.
The nutritional composition of krill supports the immense size and energetic demands of baleen whales. Krill is rich in protein and fats, providing calories for whales to grow, maintain body temperature in cold waters, and undertake long migrations. A blue whale, the largest animal on Earth, can consume up to four tons of krill daily during its feeding season.
Baleen whales typically spend several months feeding intensively in productive, high-latitude waters, storing excess energy as blubber. This stored energy sustains them during travel and breeding in warmer waters where food is less abundant. The relationship between whales and krill extends beyond consumption, as whale feces release nutrients back into the ocean, fertilizing phytoplankton blooms that krill consume. This nutrient recycling highlights the ecological dependence of baleen whales on healthy krill populations and their contribution to the marine ecosystem.