Identifying Humpback Whales—Physical Characteristics
Adult males measure 40–48 feet (12.2–14.6 meters) and adult females measure 45–50 feet (13.7–15.2 meters) in length. They weigh 25 to 40 tons (22,680–36,287 kg). Humpback whales feed on krill (small shrimp-like crustaceans) and various kinds of small fish. Each whale eats up to 1.5 tons (1,361 kg) of food a day.
|Humpback whales can be identified by their tail flukes|
Humpback whales can be identified by their tail flukesHumpbacks have a very low stubby dorsal (top) fin about two-thirds of the way back on their body. Their long front flippers, which can be one-third of the length of the body, are a key characteristic used to identify the species. The broad and serrated tail flukes have an underside showing white. When they dive deep the tail fluke will be lifted straight up—this is when researchers will take photographs for identification. When diving, humpbacks arch their backs or “hump up”—therefore the name, humpback.
The shape and color pattern on the humpback whale's dorsal fin and fluke are as individual in each animal as fingerprints in humans. Using these characteristics, individual whales are identified, catalogued and monitored—providing valuable information about such things as humpback whale population size, migration, sexual maturity and behavior patterns. If you end up with good photo ID shots on a cruise, the staff onboard can advise you where to send the images.
Distribution and Migration of Humpback Whales
|Spotting a humpback whale from a ship's deck is one of the great thrills you can have on an Antarctica cruise|
Humpback whales (Megaptera novaeangliae) are found throughout the world in all five oceans. They are known to migrate up to 15,000 miles (24,000 km) each year seeking out polar and temperate waters for feeding in the summer and warm, tropical waters for breeding in the winter months.
Estimates on the current population of humpbacks vary considerably from roughly 20,000 to 40,000. It is believed that about half of all humpbacks are found in the Southern Hemisphere with one-third in the North Atlantic and the remainder in the North Pacific. Whatever the exact population may be, it is clear that the whaling industry took a heavy toll on the species throughout the 19th and 20th centuries. Prior to the 19th century, estimates of humpback populations run as high as 1.5 million.
Humpback Whale Habitat
For both breeding and feeding, humpbacks prefer nearshore waters, but can be found traversing open waters when migrating. This preference for shallow banks means they share their habitat with recreational boaters, commercial shipping vessels and fishing nets—all of which can endanger the well-being of humpbacks.
Humpback Whale Diet
Humpbacks feed only during the summer months when they are in the nutrient-rich polar waters. During the winter breeding months, they live off their fat reserves. Their primary food source is krill (tiny shrimp-like crustaceans) and small fish, including capelin, mackerel, sand eel and herring. In a single day, an adult humpback can consume 1 to 4 tons of fish and krill. To feed, humpbacks gulp large amounts of water, expanding their throats to maximize their intake. Then they force the water out of their mouth, trapping prey in their baleen which acts like a giant strainer.
Humpback groups often work together to forage for food using a method called bubble-net feeding in which the group swims in large circles blowing bubbles. As the bubble rise to the surface of the water, they create a cylinder of air that traps prey within it. One member of the group then swims upwards through the cylinder feeding on the trapped fish.
Humpback Whale Behavior
|Spyhopping humpback whale|
Many people are familiar with the beautifully eerie vocalizations of humpback whales—often referred to as "songs." Only male humpbacks emit these vocalizations which have been the subject of much research and debate as to their "purpose"—are they threats, mating calls or some other type of communication? Vocalizations are typically heard during breeding season and are not very common when the whales are feeding in polar regions. When vocalizing, male humpbacks are often vertical in the water with their heads down, tail flukes up and front flippers extended to their sides.
Humpbacks tend to be the more active of the whales that we see during a cruise. They are well known for their thrilling breaches—they rocket out of the water, hurl two-thirds or more of their 40-ton body through air, and then crash down on the water's surface sending spray in all directions. It's not clear to researchers why humpbacks breach, but some theorize it is part of courtship display while others think it may be done purely for fun. Humpbacks also engage in a behavior called spyhopping, which entails raising their head and part of their body out of the water, presumably to scan the surface of the water in search of prey.
These curious creatures will occasionally approach our Zodiacs as we shuttle from ship to shore. Witnessing a humpback breach or seeing one at close range is an experience Antarctica travelers don't soon forget!
Humpback Whale Social Behavior
Except when breeding, humpbacks tend to live and travel alone or in small groups. These groups tend to be loose-knit and short-lived, with members coming and going frequently. When feeding, small groups of humpbacks work together to bubble-net feed.
Humpback Whale Breeding and Mating
|Humpback whales approaching a Zodiac in Antarctica|
Humpbacks whales reach sexual maturity when they are 5 to 10 years old. Adult females will bear a calf about every 2 to 3 years. Occasionally two calves are born at a time.
Courtship and breeding takes place exclusively in the warmer waters during winter months. Courtship may include a variety of behaviors, including rubbing bodies, patting with flippers, vocalizing (males only), slapping the surface of the water with pectoral flippers or tail flukes, and rolling.
The gestation period for humpbacks is about 11 months. Calves are born in warm water regions and will suckle for 6 to 10 months after birth.