The humpback whale, Megaptera novaeangliae, is a rorqual whose massive size and high energy demands necessitate specialized and highly efficient feeding mechanisms. This marine mammal must consume vast quantities of food during its feeding season to build up the necessary energy stores for its extensive annual migrations. The techniques the humpback employs range from generalized gulp feeding to highly coordinated group hunting, all focused on maximizing the intake of dense aggregations of small prey.
The Primary Prey Sources
The diet of the humpback whale depends heavily on its geographical location and the time of year. Their food sources fall into two main categories: small schooling fish and zooplankton. The schooling fish they target often include species like capelin, herring, Atlantic mackerel, and sand lance, which congregate in dense masses. They rely heavily on zooplankton, with krill being a principal food item, particularly the Antarctic krill (Euphausia superba) in the Southern Hemisphere. In northern waters, various species of Euphausia and Thysanoessa are consumed, along with copepods.
The Mechanics of Filter Feeding
Humpback whales employ a technique known as “gulp feeding” to engulf their prey. This process begins when the whale opens its mouth and lunges into a concentrated patch of prey and water. The floor of the whale’s mouth can expand dramatically due to the dozens of long, parallel ventral pleats, or grooves, running along its throat. These pleats stretch, allowing the mouth cavity to balloon out and take in a volume of water and prey that can exceed the whale’s own body mass. The whale then partially closes its mouth and uses its massive tongue to push the water out. The water is forced through hundreds of overlapping baleen plates that hang from the upper jaw. These plates, made of keratin, have fine, hair-like fringes on the inner edge that act as a sieve. The water escapes through this filter, trapping the small fish and krill against the baleen. Once the water is expelled, the whale swallows the concentrated mass of food.
The Unique Strategy of Bubble-Net Feeding
Humpbacks have developed a behavioral strategy called bubble-net feeding, a remarkable form of cooperative hunting. This technique often involves multiple whales working together to corral their prey into a dense formation. The process begins with one or more whales diving beneath a school of fish or krill. As they circle their prey, the whales exhale a continuous stream of air bubbles from their blowholes, creating a rising, cylindrical curtain. This wall of bubbles acts as a visual and acoustic barrier, herding the prey toward the surface in a tightly packed column. Once the prey is sufficiently concentrated near the surface, the whales simultaneously surge upward through the center of the bubble column, mouths open wide. This coordinated lunge allows them to engulf a maximum amount of food with a single, highly efficient gulp. Studies have shown this technique can allow the whales to capture up to seven times more prey than a solitary feeding attempt.
The Seasonal Feeding Cycle
The feeding habits of the humpback whale are linked to its annual migratory cycle. Humpbacks spend the summer and fall months in high-latitude polar waters, such as those off Alaska or Antarctica, where the abundance of krill and fish is at its peak. This intense feeding phase requires the whale to consume up to 1.5 tons (3,000 pounds) of food daily. The purpose of this consumption is to build up a thick layer of blubber, which serves as a massive energy reserve. The whales then undertake an extensive migration to warmer, low-latitude tropical waters for their breeding season. During this period, which can last up to eight months, the humpbacks largely fast. They survive almost entirely on the fat reserves accumulated during the feeding season, losing between 25 and 50 percent of their body mass.