A whale's diet depends on the species of whale and the ecosystem in which it lives. Ironically, some of the largest whale species subsist on the tiniest of marine life. Many whales consume fish, while other whales are large-scale predators of seals and penguins. Generally, whales are divided into two categories: baleen or toothed. The baleen whales have plates that act as filters in their mouths, allowing nothing larger than small krill and plankton into their mouths, while toothed whales survive by hunting larger prey.
Each individual krill weighs only 1 to 2 grams. Yet, cumulatively, krill make up one of the largest biomass of any animal species on the planet. These tiny crustaceans are the primary food source for many filter-feeding species of whales that inhabit the Arctic and Antarctic, including the endangered blue whale and humpback whale, as well as the minke whale.
Phytoplanktons are tiny single-celled algae close to the surface of the ocean, which zooplanktons eat. Phytoplankton is a major food source for baleen whales. Bowhead whales, gray whales and right whales all survive on a combination of phytoplankton and zooplankton.
Zooplanktons are tiny animals and crustaceans, such as copepods and rotifers, as well as the larval stages of larger fish and crustaceans (including krill larvae), which feed on phytoplankton. All filter-feeding baleen whales, such as fin whales and sei whales, consume zooplankton.
Fish, Squid, and Shrimp
Though filter-feeding whales may eat very small fish, the toothed whales such as pilot whales, dolphins and belugas, hunt fish, squid and shrimp. Toothed whales eat a variety of fish, from bottom-dwelling halibut to surface-swimming salmon. They also frequently prey on hake, cod, herring and smelt. According to the NOAA Fisheries, the sperm whale diet consists mainly of large squid, but sperm whale will also eat large sharks, skates and fishes.
Marine Mammals and Birds
The most famous predatory whale is the orca, also called the "killer whale." Orcas are toothed whales, which hunt not only fish, shrimp and squid, but even penguins, seals and other whales. According to SeaWorld, orcas eat marine mammals such as sea lions, seals, walruses and sea otters, as well as baleen whales and toothed whales. Examinations of the stomach contents of orcas have discovered reptiles, polar bears and even a moose..