Blue Whale – Balaenoptera musculus

Common Name: Blue Whale
Scientific Name: Balaenoptera musculus
Classification: Kingdom Animalia → Phylum Chordata → Class Mammalia → Order Cetacea → Family Balaenopteridae → Genus Balaenoptera → Species musculus
IUCN Conservation Status: Endangered (EN)

Subspecies:

1. Balaenoptera musculus musculus – North Atlantic and North Pacific populations
2. Balaenoptera musculus intermedia – Antarctic Blue Whale
3. Balaenoptera musculus brevicauda – Pygmy Blue Whale (the resident subspecies found around Sri Lanka)

Geographic Range (where the species is found):

The Blue Whale is cosmopolitan, found in all major oceans except the Arctic. The Pygmy Blue Whale (B. m. brevicauda), inhabits tropical and subtropical waters of the Indian and South Pacific Oceans. Around Sri Lanka, this subspecies forms a resident population concentrated in the southern, southeastern, and eastern coastal waters, especially near Mirissa, Galle, Batticaloa, and Trincomalee. These areas are associated with strong upwelling systems that support dense krill populations.

Description:

The Blue Whale is the largest animal on Earth, reaching 24–30 meters in length and weighing up to 150 tonnes. Its body is long, streamlined, and bluish-gray with mottled patterns unique to each individual. The head is broad and flat, with a single ridge running from the blowholes to the snout. The dorsal fin is small and set far back, and the blow rises in a tall vertical column reaching up to 12 meters.
The Pygmy Blue Whale is smaller (20–24 meters), with a proportionally larger dorsal fin and shorter body. The throat has 60–90 grooves, which expand during feeding. Baleen plates (about 300 per side) are black with fine bristles for filtering krill.

Habitat:

Occupies deep offshore waters, often along continental slopes and upwelling zones rich in plankton. Around Sri Lanka, Blue Whales are strongly associated with warm, nutrient-rich waters in the southern and eastern coasts, which support year-round feeding.

Diet:

Carnivore (filter feeder).
Feeds almost exclusively on krill (Euphausiids), occasionally consuming copepods and small schooling fish. During feeding, it can engulf up to 70 tonnes of water in a single gulp, using baleen plates to strain prey and expel water.

Ecological Role of Balaenoptera musculus:

A keystone marine species, Blue Whales help maintain oceanic food web balance by controlling krill populations. Their nutrient-rich fecal plumes contribute to iron fertilization, stimulating phytoplankton growth, which supports entire marine ecosystems and aids carbon sequestration.

Life Cycle:

Blue Whales have a long lifespan of 70–90 years. Calves are born after a 10–12 month gestation period, measuring about 7–8 meters and weighing around 3 tonnes. They grow rapidly, nursing for 6–7 months and gaining up to 90 kg daily. Sexual maturity is reached between 8–10 years of age.

Reproduction (mating season, number of offspring):

Breeding typically occurs in winter months within tropical waters. Females give birth to one calf every 2–3 years. Unlike migratory populations, the Pygmy Blue Whales of Sri Lanka breed and feed in the same tropical region year-round.

Behaviour:

Generally solitary or found in pairs, though small feeding groups may form seasonally. Blue Whales are slow-moving but capable of short bursts of speed when disturbed. They produce low-frequency vocalizations (10–40 Hz) that can travel hundreds of kilometers, used for communication and navigation. Around Sri Lanka, individuals are observed feeding, diving, and occasionally breaching—a rare behavior for the species.

Key Adaptations:

• Massive size for thermoregulation and predator deterrence.
• Expandable throat pleats allowing huge prey intake.
• Efficient oxygen storage in muscles for deep, prolonged dives.
• Low-frequency calls enabling long-distance communication.
• Non-migratory adaptation in tropical Pygmy subspecies, exploiting local productivity.

Threats:

• Ship strikes, especially along the busy southern shipping lane near Sri Lanka.
• Noise pollution disrupting communication and behavior.
• Entanglement in fishing gear.
• Plastic ingestion and marine debris pollution.
• Climate change, affecting krill distribution and monsoon-driven productivity.
• Chemical contaminants impacting reproductive health.
  While global populations are recovering from commercial whaling, regional populations remain vulnerable and small.

Interesting Fact:

The Blue Whale’s heart weighs about 180 kg and its tongue can weigh as much as an elephant. Despite its enormous size, it feeds almost exclusively on tiny krill. Sri Lanka is one of the only places in the world where Blue Whales can be seen year-round, making it a global hotspot for marine megafauna research and ecotourism.

REFERENCES

• Wikipedia – Blue Whale — overview of taxonomy, size, distribution. (Wikipedia)
• NOAA Fisheries – Blue Whale — U.S. gov. species profile with biology & conservation. (NOAA Fisheries)
• NAMMCO – Blue Whale — North Atlantic Marine Mammal Commission data on the species. (NAMMCO)
• IUCN Red List – Balaenoptera musculus — global conservation status.
• OBIS-SEAMAP – Balaenoptera musculus — taxonomic and occurrence data. (seamap.env.duke.edu)
• WWF Australia – Blue Whale — species profile and distribution. (wwf.org.au)

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