Whales, like humans, are mammals. They are warm-blooded, meaning they maintain a constant body temperature (37°C). They have lungs and breathe air. When whales adapted to living in whater nostrils evolved into blowholes and are now located at the top of the head. Front limbs have transformed into pectoral fins; the humerus, radius, ulna, metacarpals and phalanges are all present. The hind limbs and pelvic structure have disappeared almost completely, supporting contraction muscles
Their offspring develop in the mother’s womb, are nourished by the placenta during pregnancy and are nursed after birth. The body is streamlined and has lost its fur and nearly all its hair. The tail has transformed into a powerful horizontal fluke attached to the vertebral column. Modern whales thus look very different from their closest living relatives.
Toothed whales and baleen whales:
The availability of a wide range of food sources in the world‘s oceans led to the evolution of two cetacean suborders: baleen whales, which use their baleen plates to filter small organisms out of the water, and toothed whales, which may capture larger, individual prey with their teeth. Collectively they feed on prey species at practically every level in the marine ecosystem.
The baleen plates form an efficient filtration system that separates the prey from seawater. To feed, the whales open their mouths to engulf water and food, then close it partially to force the water out through the baleen plates. The trapped food is scraped off with the tongue and swallowed.
Equipped with expandable throat grooves, the rorquals, such as blue, fin, sei, minke and humpback whales, are able to engulf large volumes of water. The so-called gulping facilitates catching of small and mobile organisms like krill. Blue whales can take up to 50 tons of water in a single gulp.
As tooth whales teeth are mostly conical, they are used to grasp or tear, but not to chew. It is likely that suction feeding plays an important role in capturing prey for toothed whale species with few or no teeth. The prey is sucked in through a sudden pressure drop partially caused by retraction of the tongue. Whale teeth show growth rings, from which the animal’s age can be determined.
What do whales eat:
The availability of a wide range of food sources in the world‘s oceans led to the evolution of two cetacean suborders: baleen whales, which use their baleen plates to filter small organisms out of the water, and toothed whales, which may capture larger, individual prey with their teeth. Collectively they feed on prey species at practically every level in the marine ecosystem.
Baleen whales feed on the most abundant food in the ocean, zooplankton, along with krill, copepods, herring, sandeel and capelin. Gray and bowhead whales additionally feed on a wide variety of other invertebrates such as amphipods and shellfish.
The baleen plates form an efficient filtration system that separates the prey from seawater. To feed, the whales open their mouths to engulf water and food, then close it partially to force the water out through the baleen plates. The trapped food is scraped off with the tongue and swallowed.
The kind of prey taken by toothed whales is often related to their body size and number of teeth. Their main diet consists of fish, such as herring, sandeel, cod, halibut, tuna, shark, and squid.
As whales‘ teeth are mostly conical, they are used to grasp or tear, but not to chew. Species such as sperm and beaked whales, with few or no erupted teeth, or teeth only in the lower jaw, tend to eat soft-bodied prey such as squid.
Whale teeth show growth rings, from which the animal’s age can be determined. Cetaceans have a four-chambered stomach to better digest unchewed food. The forestomach is kept in motion by muscle tissue and often contains sand, pebbles and shells, helping in the crushing of food.
Whales satisfy their need for water intake mostly with food. The salt from the water inhaled with prey is extracted and the water is conserved in their kidneys, which have a high efficiency in concentrating urine.
Fun fact: The main diet of sperm whales consists of squid of various sizes. The sharp squid beaks are indigestible and often accumulate in the stomach of the whale, causing irritation and the formation of a thick liquid in the whale’s intestines. After being excreted, the liquid turns into a waxy, aromatic substance called ambergris. In earlier times, ambergris was highly valued and used for the production of perfume. Synthetic substances have now replaced its attributes and trade in ambergris is banned worldwide by treaty.
How do whales eat?
Toothed whales feed throughout the year and stay in regions where prey is available at all times. For most of the baleen whales, feeding takes place in feeding grounds. During that time, the weight gain averages around 40% of their body weight, which is stored in the blubber and then gradually lost during the rest of the year as it is used for energy. During the winter, baleen whales spend between six and eight months travelling to the tropical waters and giving birth. Throughout this time baleen whales eat much less or even not at all as there is much less food available.
Equipped with expandable throat grooves, the rorquals, such as blue, fin, sei, minke and humpback whales, are able to engulf large volumes of water. The so-called gulping facilitates catching of small and mobile organisms like krill. Blue whales can take up to 50 tons of water in a single gulp.
Right and bowhead whales have the largest baleen plates, with the finest hairs. This allows them to filter out zooplanktonic organisms, which are typically the size of a rice grain. They feed by swimming along the ocean surface with their mouths open, a feeding technique called skimming.
Gray whales, with the smallest baleen plates, are primarily bottom feeders. They stir up the ocean floor close to shore, using their lower jaw, and filter the sediment in search of amphipods.
Among the most interesting foraging techniques are the bubble nets that humpback whales blow to trap fish. Whales dive deep below schools of fish and use bubbles blown from their blowholes to stun and trap fish closer to the surface. One whale generally leads the hunt, followed by the rest of the group. The leader will usually be responsible for blowing the bubbles and the other members will surround the fish, following them to the surface by swimming in spiral patterns to keep the fish trapped. During bubble-net feeding, the whales swimming toward the surface will have their mouths open and gulp fish from the school they have corralled.