Baleen whales, a group of marine mammals, differ from toothed whales due to their specialized filter-feeding strategy. These colossal creatures, like the blue and humpback whale, lack teeth, instead using a distinctive internal structure to process vast quantities of water and efficiently extract food. This adaptation allows them to thrive on the ocean’s smallest organisms, sustaining their large sizes.
The Baleen Filtration System
Baleen consists of plate-like structures hanging from the upper jaw, composed of keratin—the same protein as human fingernails and hair. Each plate has fine, hair-like fringes along its inner edge, forming a dense, sieve-like mat.
When feeding, a baleen whale takes in a large volume of water and prey. Water is then expelled through the baleen plates, with fringed edges filtering and trapping food. Baleen coarseness varies by species, reflecting dietary preferences. For example, whales feeding on smaller organisms like zooplankton have longer plates with finer fringes.
Diverse Feeding Strategies
Baleen whales use various methods to capture prey, tailored to their environment and food.
Gulp Feeding
Gulp feeding, or lunge feeding, is used by rorqual whales such as humpbacks, blue whales, and fin whales. These whales accelerate, open their mouths to engulf large volumes of water and prey, then rapidly expel the water through their baleen, trapping food inside. They can take in a volume of water equivalent to a school bus in a single gulp, aided by throat pleats.
Skim Feeding
Skim feeding is used by right whales and bowhead whales. They swim slowly through dense plankton patches with open mouths, allowing water to flow through their baleen. Forward movement pushes water through the baleen, trapping prey. Right whales have long, fine baleen to filter small zooplankton like copepods.
Bottom Feeding
Gray whales use a bottom-feeding or “dredging” strategy. They turn onto their side in shallow waters, using their muscular tongues to suck up sediment, water, and benthic organisms from the seafloor. Water and sediment are filtered through their baleen, and trapped invertebrates swallowed. This behavior often leaves visible furrows on the ocean floor.
Primary Prey and Nutritional Significance
Baleen whales primarily consume organisms low on the marine food chain, such as zooplankton and small schooling fish. Krill, small shrimp-like crustaceans, are a major component for many species, including blue and humpback whales. Other common prey include copepods, a staple for right whales, and small schooling fish such as herring or anchovies.
A blue whale, for example, can consume up to 3,600 kilograms (approximately 8,000 pounds) of krill daily during its feeding season, which lasts about four to six months. Gray whales can eat around 150,000 kilograms (approximately 340,000 pounds) of food over a 130 to 140-day feeding period.
This high-energy intake is stored as blubber, a thick layer of fatty tissue beneath the whale’s skin. Blubber serves as an energy reserve, insulating the whale in cold waters and providing sustenance during long migrations and breeding seasons when food is scarce. Gray whales can gain 16% to 30% of their body weight during feeding season, with blubber making up a significant portion of their total body mass (21% in sei whales to 45% in right whales).