Audience:Pods of blue whales have found a unique home in the tropical waters of Sri Lanka. The island’s geology and climate create conditions that allow these gentle giants to stay close to shore almost year-round.The continental shelf surrounding Sri Lanka is unusually narrow. A continental shelf is a geologic feature that extends from a shoreline to a steep drop-off known as a shelf break. A narrow continental shelf means large, deep-water species such as blue whales can safely swim very near the shore.Two climate conditions also favor Sri Lanka’s blue whales. The first is upwelling, an underwater process in which cold, nutrient-rich water from the deep ocean is forced toward the surface. Upwellings fill the ocean around Sri Lanka with krill, the staple of a blue whale’s diet.The second climate condition that creates such a rich environment for blue whales around Sri Lanka is the “double monsoon.” A double monsoon describes seasonal climates impacted by strong, predictable changes in prevailing wind patterns (monsoons). The summer monsoon brings winds from the hot, humid southwestern Indian Ocean. The summer monsoon is associated with torrential rainfall and warm surface waters. The winter monsoon brings cooler, drier air from the Himalayas, far to Sri Lanka’s north. Winter monsoons are much, much less powerful than summer monsoons in Sri Lanka, but the mixing of ocean waters creates opportunities for upwelling and creates a diverse marine ecosystem in which the blue whale thrives.Watch the video, from the Nat Geo WILD series “Destination Wild,” to learn about other environmental conditions that allow southern Sri Lanka to support one of the world’s largest populations of pygmy blue whales. Use the Fast Facts tab to learn some interesting facts about this distinct subspecies. Be sure to listen to vocalizations in the video, and see if you can answer questions about blue whale “songs” in the Questions tab.
What is a “whale song”?
Why do whales “sing”?
Why are the songs of Sri Lanka’s blue whales so unusual?
- Pygmy blue whales, the subspecies found around southern Sri Lanka, inhabit all the world’s ocean basins, although they seem concentrated in the Indian and South Pacific. Many populations migrate to Antarctica, but the Sri Lanka population seems to pretty much stay put, forming what marine biologists call a “resident population.”
- As their name indicates, pygmy blue whales are slightly smaller than their big blue siblings. Pygmies reach lengths of about 24 meters (79 feet), while “true blues” reach lengths of 30 meters (98 feet).
- The heads of pygmy blue whales are nearly the same size as “true blues,” but their tails are shorter. So, while “true blues” have an elongated torpedo shape, pygmies have a stumpier, head-heavy tadpole shape.
- “True blues” are an endangered species, but there isn’t enough information about pygmies to classify them in a threatened category. Experts think there are between 5,000 and 10,000 pygmy blue whales swimming the ocean today.
- The biggest threats to pygmy blue whales are whaling, climate change (which impacts feeding patterns), noise interference (which interrupts communication) and "vessel disturbance"—being hit by container ships.
Term Part of Speech Definition Encyclopedic Entry climate Noun
all weather conditions for a given location over a period of time.
Encyclopedic Entry: climate climate change Noun
gradual changes in all the interconnected weather elements on our planet.
Encyclopedic Entry: climate change communicate Verb
to exchange knowledge, thoughts, or feelings.
continental shelf Noun
part of a continent that extends underwater to the deep-ocean floor.
Encyclopedic Entry: continental shelf diet Noun
foods eaten by a specific group of people or other organisms.
Encyclopedic Entry: diet endangered species Noun
organism threatened with extinction.
Encyclopedic Entry: endangered species environment Noun
conditions that surround and influence an organism or community.
rate of occurrence, or the number of things happening in a specific area over specific time period.
study of the physical history of the Earth, its composition, its structure, and the processes that form and change it.
air containing a large amount of water vapor.
body of land surrounded by water.
Encyclopedic Entry: island isolation Noun
separation from other people, habitats, or communities.
small marine crustacean, similar to shrimp.
marine ecosystem Noun
community of living and nonliving things in the ocean.
seasonal change in the direction of the prevailing winds of a region. Monsoon usually refers to the winds of the Indian Ocean and South Asia, which often bring heavy rains.
Encyclopedic Entry: monsoon nutrient Noun
substance an organism needs for energy, growth, and life.
Encyclopedic Entry: nutrient ocean basin Noun
depression in the Earth's surface located entirely beneath the ocean.
group of whales or dolphins.
prevailing wind Noun
wind that blows from one direction.
shelf break Noun
underwater edge of a continental shelf, where it begins a rapid slope to the deep ocean floor.
(subsp.) group of organisms within a single species, often distinguished by geographic isolation.
threatened categories Noun
three levels of endangered species: vulnerable, endangered, and critically endangered.
to develop and be successful.
existing in the tropics, the latitudes between the Tropic of Cancer in the north and the Tropic of Capricorn in the south.
process in which cold, nutrient-rich water from the bottom of an ocean basin or lake is brought to the surface due to atmospheric effects such as the Coriolis force or wind.
Encyclopedic Entry: upwelling vocalization Noun
sound or noise made by the vocal chords of an organism.
industry of hunting whales.