Whales, diverse marine mammals inhabiting the world’s oceans, exhibit a wide array of feeding strategies. Their diet often raises questions, particularly regarding zooplankton consumption. Indeed, some whales, known as baleen whales, primarily feed on these tiny organisms, a unique adaptation for gathering vast quantities of small prey.
Whales That Consume Zooplankton
Whales are broadly categorized into two groups based on their feeding mechanisms: toothed whales (Odontoceti) and baleen whales (Mysticeti). Toothed whales, like sperm whales, orcas, and dolphins, hunt individual prey such as fish, squid, and other marine mammals, using their teeth. Baleen whales lack teeth and filter-feed, straining small organisms from large water volumes.
This group includes some of the ocean’s largest inhabitants, such as blue whales, humpback whales, fin whales, right whales, and bowhead whales. Their diet primarily consists of zooplankton and small schooling fish, which they encounter in dense aggregations. For instance, blue whales predominantly feed on krill, while right whales specialize in consuming smaller crustaceans called copepods. Gray whales exhibit a unique feeding behavior, sifting through bottom sediments for crustaceans and marine worms.
The Mechanism of Filter Feeding
Baleen whales consume zooplankton using specialized baleen plates. These keratin plates hang from the whale’s upper jaw. Each plate has fine, fringed edges that interlock to form a sieve-like structure, allowing water to pass through while trapping food particles.
Baleen whales employ different filter-feeding techniques. Gulp feeding, also known as lunge feeding, is characteristic of rorqual whales like blue whales and humpback whales. These whales accelerate, open their mouths wide to engulf massive amounts of water and prey, causing their pleated throat grooves to expand significantly. The whale then closes its mouth, contracts its throat, and uses its tongue to force the water out through the baleen, retaining the concentrated prey.
Another method is skim feeding, primarily used by right whales and bowhead whales. These whales swim slowly through the water with their mouths continuously open, allowing water to flow through their baleen plates. The fine baleen of these species is particularly effective at filtering out tiny zooplankton like copepods as the whale moves. This continuous filtration method is efficient for harvesting dispersed prey.
Zooplankton’s Place in the Ocean Ecosystem
Zooplankton are microscopic marine animals that drift with ocean currents. This diverse group includes copepods, krill, and other larval organisms. Zooplankton are heterotrophic, meaning they obtain nutrients by consuming other organisms, primarily phytoplankton (plant-like plankton that harness energy from sunlight).
They represent the second trophic level in marine food webs, acting as primary consumers. Their role is to convert phytoplankton’s energy into a form accessible to larger animals. Zooplankton are abundant, forming the base of many oceanic food webs.
This abundance makes zooplankton a highly energy-rich food source, enabling baleen whales to meet their substantial caloric requirements. During feeding seasons, large baleen whales can consume up to 4% of their body weight daily. For example, a blue whale can consume approximately 17.6 tons of krill in a single day. Whale waste products, particularly iron-rich feces, also contribute to nutrient recycling, fertilizing phytoplankton blooms and supporting the marine ecosystem.