The fin whale, Balaenoptera physalus, is the second-largest animal on Earth, surpassed in size only by the blue whale. As a member of the rorqual family, this streamlined marine mammal is built for speed and immense feeding capacity. Adults reach lengths over 80 feet and weights up to 80 tons, demanding a consistent and high-volume intake of calories. The sheer energy needs of such a massive creature have driven the evolution of a specialized feeding strategy focused on consuming dense masses of small organisms.
Primary Components of the Fin Whale Diet
The diet of the fin whale is primarily composed of small, calorie-rich organisms that aggregate in vast, concentrated schools or swarms. These prey items fall into two main categories: small crustaceans and small schooling fish.
Krill forms a substantial portion of the fin whale’s energy source, especially in high-latitude feeding grounds. Specific species of krill, such as Euphausia superba in the Southern Ocean and various species like Thysanoessa inermis and Euphausia pacifica in the Northern Hemisphere, are a staple. Fin whales also consume copepods, particularly those from the genus Neocalanus in the North Pacific.
When krill and copepods are less available, or in certain geographical regions, the fin whale preys on dense schools of small pelagic fish. Examples of these schooling fish include Atlantic herring (Clupea harengus), capelin (Mallotus villosus), and sand lance (Ammodytes species). These fish are energy-dense, providing the high caloric return necessary to sustain the whale’s body mass. An adult fin whale may consume as much as 4,000 pounds of food per day during the intense feeding season.
The Mechanics of Lunge Feeding
Fin whales utilize a method known as lunge feeding to capture their prey. This process involves a rapid acceleration toward a dense patch of prey. The whale opens its mouth to a gape of up to 80 degrees, allowing it to engulf an enormous volume of water and prey.
The primary adaptation for this feeding style is the highly elastic throat. Longitudinal ventral grooves, or pleats, run from the chin to the navel, enabling the entire buccal cavity to expand dramatically. This expansion allows the whale to take in a volume of water that can be larger than the whale itself, due to the flexibility of the blubber and muscle tissue.
Once the water and prey are engulfed, the whale slows down and closes its jaws, initiating the filtration process. It uses baleen plates, which hang from the upper jaw, to filter the contents. These keratin plates have fine, hair-like fringes that trap the prey while the massive volume of water is forced out through the sides of the mouth. The concentrated mass of food is then swallowed.
How Location and Season Affect Prey Choice
The fin whale’s diet is heavily influenced by its annual migration cycle and the local availability of prey. Fin whales undertake long-distance migrations, intensely feeding in productive, high-latitude polar regions during the summer months. This concentrated feeding builds up the extensive fat reserves required to sustain them through migration and the winter breeding season in lower latitudes, where feeding is significantly reduced or stops entirely. The specific prey consumed often shifts based on the whale’s current geographical location. For example, fin whales in the North Atlantic may feed on a different mix of krill species and small fish like capelin and herring than those in the Southern Ocean, which primarily target Antarctic krill (E. superba). Fin whales are opportunistic feeders, switching their diet to whatever small, schooling organism is most abundant in a given area. This adaptability ensures a continuous, high-energy intake throughout the productive summer season.