Anatomy and Physiology: What the Numbers Don't Say
Everyone knows the measurements of the blue whale: up to 33 m for the largest Antarctic specimens, 100 to 150 tonnes for adults. But these raw figures hide remarkable biological mechanisms.
Gray-Blue Coloration and Light Spots
The skin is slate-gray, dotted with irregular light spots. Underwater, light diffusion in the superficial layers gives the animal an intense blue hue, the origin of its common name. This spot pattern is individual: it forms the basis of photo-identification used by researchers and citizen platforms like Happywhale.
Baleen and Krill Feeding
The blue whale is a mysticete: it has no teeth but 300 to 400 pairs of black baleen plates, 50 to 100 cm long, which filter the water. The feeding technique is lunge feeding: the animal accelerates, opens its mouth, engulfs a colossal volume of water, then expels the water while retaining the krill (Euphausiacea spp.) against the baleen. An adult can ingest up to 4 tonnes of krill per day during intense feeding periods (GREMM, compiled data).
Heart, Lungs, and Diving
The blue whale's heart weighs about 180 kg and beats at 4 to 8 beats per minute during dives, versus 25 to 37 at the surface. This diving bradycardia reduces oxygen consumption. Dives rarely exceed 200 m in depth because krill concentrates in superficial layers, but their duration can reach 20 minutes.
Infrasonic Vocalizations
The vocalizations of the blue whale are among the most powerful in the animal kingdom: they reach 188 decibels and range between 10 and 40 Hz, below the human hearing threshold. These infrasounds propagate over hundreds, even thousands of kilometers in the ocean. Their exact role remains debated: long-distance communication between individuals, locating breeding partners, orientation, probably a combination of the three (Croll et al., 2002).
Subspecies and Populations: One Species, Multiple Realities
Blue whale taxonomy is often simplified in popular sources. Three subspecies are recognized, plus one population with distinct behavioral traits. This distinction has direct implications for actual population sizes and conservation priorities.
True Blue Whale (B. m. musculus): North Atlantic and North Pacific
This is the nominate subspecies, the largest. It frequents the North Atlantic, notably the St. Lawrence, and the North Pacific, with concentrations off California and Mexico. Its global population is estimated at just a few thousand individuals (IUCN, 2018).
Pygmy Blue Whale (B. m. brevicauda): Indian Ocean and South Pacific
Slightly shorter (generally 20 to 24 m), it is distinguished by a proportionally longer tail and a more massive caudal region. It mainly frequents the Indian Ocean and South Pacific. Its population is considered numerically larger than that of the nominate subspecies, but data remain fragmentary.
Antarctic Blue Whale (B. m. intermedia): Southern Waters
This is the largest subspecies and the most affected by 20th-century industrial whaling. Southern waters once hosted hundreds of thousands of individuals. Current estimates indicate fewer than 2,000 individuals, making it the most threatened population (IUCN, 2018). Its recovery is extremely slow.
Sri Lanka Population: Partial Sedentary Behavior
The population frequenting Sri Lanka waters, notably off Mirissa, shows unusual behavior: part of the individuals appear resident year-round, without undertaking the long polar migrations typical of the species. Local operators and researchers from the Sri Lanka Blue Whale Project document this partial sedentariness, which remains poorly explained and potentially linked to local krill availability.
Identifying a Blue Whale from a Boat: Blow, Dorsal Fin, Behavior
At sea, identifying large rorquals requires method. Here are the criteria I use systematically, in the order they become visible on approach.
The Blow: Height, Shape, and Verticality
This is often the first sign. The blue whale's blow is very vertical, narrow, and can exceed 9 m in height. It is visible from afar in calm weather. A short, diffuse, or angled blow points to another species. Verticality is the most reliable criterion at long range.
The Dorsal Fin: Small, Far Back
The blue whale's dorsal fin is small (about 30 cm high) and positioned in the last quarter of the body, very close to the tail. It appears only after the blow has dissipated, during the dive descent. This is an essential distinguishing criterion compared to the fin whale (Balaenoptera physalus), whose fin is larger and more forward.
The Tail During Diving
Unlike the sperm whale (Physeter macrocephalus), the blue whale rarely shows its fluke (tail) during dives. When it does, it is generally during deep dives, which remain rare in coastal feeding areas. The absence of a visible fluke is thus an additional clue, but not absolute.
Comparison Table
| Criterion | Blue Whale | Fin Whale | Bryde's Whale |
|---|---|---|---|
| Adult Length | 24-33 m | 18-27 m | 12-15 m |
| Blow | Vertical, 9 m+ | Vertical, 6-8 m | Shorter, more diffuse |
| Dorsal Fin | Small, far back | Larger, more forward | Sickle-shaped, prominent |
| Coloration | Uniform gray-blue | Asymmetric white right side | Uniform dark gray |
| Fluke Visible | Rarely | Rarely | Rarely |
Where and When to Observe the Blue Whale: Reference Sites
I haven't observed the blue whale from Camaret, and for good reason: the species is absent from Breton waters. The following data come from operator reports, GREMM publications, and IUCN site fact sheets.
St. Lawrence (Quebec)
The St. Lawrence is one of the world's best-documented sites for the species. According to the GREMM (Group for Research and Education on Marine Mammals), blue whales frequent the estuary from June to October, peaking in August. The Tadoussac and Pointe-Noire area concentrates sightings. Canadian regulations impose a minimum distance of 400 m for endangered species in this zone.
Azores
The Azores' geographic position, at the crossroads of several Atlantic migration routes, makes it Europe's most reliable site. Certified local operators report regular sightings from March to June. Several companies adhere to the High Quality Whale Watching (HQWW) charter, facilitating the choice of a responsible operator.
Sri Lanka (Mirissa)
Waters off Mirissa concentrate blue whales from November to April. Field observers report high densities but also concerning overcrowding: dozens of boats can surround the same animal simultaneously. Local NGOs and Whale and Dolphin Conservation regularly alert on non-compliance with minimum distances (WDC, annual reports).
Baja California (Mexico)
The Sea of Cortez and Baja California coastal waters host blue whales from January to March, come to feed on krill. Operators from La Paz and Loreto offer guided trips. Coastal concentration facilitates sightings but also exposes animals to collision risks with maritime traffic.
Iceland and Antarctica
In Iceland, sightings are reported sporadically north and west of the island, mainly in summer, but they remain rare and not guaranteed. In Antarctica, polar cruises sometimes allow observation of the B. m. intermedia subspecies, but weather conditions and Antarctic Treaty regulations impose significant logistical constraints.
Conservation Status: Between Legal Protection and Persistent Threats
The blue whale has enjoyed international protection since 1966, when the International Whaling Commission (IWC) banned commercial hunting. Fifty years later, the global population has not recovered to historic levels.
Historic Numbers and Impact of Industrial Whaling (1900-1966)
Before industrial whaling, the global blue whale population is estimated at 200,000 to 300,000 individuals. Between 1900 and 1966, over 360,000 animals were killed, mainly in the Southern Hemisphere (IWC data, compiled by IUCN). The Antarctic subspecies was the most affected, with annual takes exceeding 30,000 individuals in some years.
IUCN "Endangered" Status: Current Figures
The IUCN classifies the blue whale as "Endangered" since 2018. The total global population is estimated between 10,000 and 25,000 individuals, all subspecies combined (IUCN, 2018). This figure represents less than 10% of pre-industrial numbers. Recovery is slow: a female produces only one calf every 2 to 3 years, and sexual maturity is reached around 10 years.
Ship Strikes: Leading Human-Caused Mortality
Today, ship strikes are identified as the leading human-caused mortality factor for the species (Redfern et al., 2013). Commercial shipping routes directly cross feeding and migration areas in the Northeast Pacific, Sri Lanka, and the Mediterranean. Route shifts or speed reductions have been tested in California and the St. Lawrence, with encouraging but insufficient results.
Noise Pollution, Entanglement, and Climate Change
Noise pollution from maritime traffic disrupts infrasonic vocalizations, potentially reducing long-distance communication capacity. Entanglement in fishing gear remains rare but documented. Climate change alters krill distribution, forcing animals to change migration routes and expend more energy to find food (Hazen et al., 2013).
Observation Ethics and Regulatory Distances
Observing a blue whale from a boat is a privilege that entails concrete responsibilities. The rules are not abstract recommendations: they respond to documented stress and flight behaviors in animals approached too closely.
Recommended Minimum Distances
The High Quality Whale Watching (HQWW) charter recommends a minimum distance of 100 m for large cetaceans. In Canada, in the St. Lawrence, regulations impose 400 m for species listed as "endangered," including the blue whale (Species at Risk Act, Canada). In Sri Lanka, no binding national regulations existed as of 2023, explaining the documented overcrowding at Mirissa.
Behaviors to Avoid
Head-on approaches are particularly stressful: they cut across the animal's path and can provoke abrupt course changes. Engine running in close proximity generates vibrations and underwater noise. Unregulated drones flying low over the animal disrupt breathing and surface behavior. These three behaviors are explicitly discouraged by the HQWW charter and Whale and Dolphin Conservation.
Choosing a Responsible Operator
Before boarding, I recommend checking adherence to the HQWW charter or equivalent label, asking if a trained naturalist is on board, and ensuring the operator clearly communicates on distances respected. A serious operator refuses to guarantee sightings and does not pursue an animal that moves away.
Contributing to Citizen Science
Every clear photo of a blue whale's dorsal fin or spot pattern can be submitted to Happywhale or Obs-MAM for photo-identification. These platforms track identified individuals' movements over years and thousands of kilometers. This is a concrete contribution to research, accessible to any observer with a camera offering at least 300 mm equivalent focal length.
Frequently asked
What is the maximum size of a blue whale?
Females generally reach 24 to 27 m. The largest measured specimen, caught in Antarctica, exceeded 33 m. Adult weight ranges from 100 to 150 tonnes (GREMM, compiled data). The pygmy subspecies (B. m. brevicauda) is shorter, averaging 20 to 24 m.
Is the blue whale still threatened with extinction?
Yes. The IUCN classifies it as "Endangered" since 2018. The global population is estimated at 10,000 to 25,000 individuals, versus hundreds of thousands before industrial whaling (IUCN, 2018). Recovery is slow due to a very low reproduction rate and persistent threats like ship strikes.
How to distinguish a blue whale from a fin whale at sea?
The blue whale's blow is very vertical and can exceed 9 m in height. Its dorsal fin is small and far back toward the tail. The fin whale (Balaenoptera physalus) has a larger, more forward fin and shows asymmetric coloration on the right lower jaw visible at close range.
Where to observe the blue whale in Europe?
The Azores are Europe's most reliable site, especially from March to June, thanks to their position at the crossroads of Atlantic migration routes. Sporadic sightings are reported in the western Mediterranean and off Iceland, but they remain rare and not guaranteed by local operators.
What minimum distance to maintain during boat observation?
The High Quality Whale Watching charter recommends a minimum of 100 m for large cetaceans. In Canada, in the St. Lawrence, regulations impose 400 m for endangered species, including the blue whale. These distances are non-negotiable: getting closer disrupts the animal's behavior and may be illegal depending on jurisdiction.
What does the blue whale eat and in what quantity?
It feeds almost exclusively on krill (small crustaceans of the Euphausiacea group). During intense feeding periods, an adult can ingest up to 4 tonnes of krill per day, using shallow filtration dives via lunge feeding (GREMM, compiled data).
Is the pygmy blue whale a different species?
No, it is a subspecies: Balaenoptera musculus brevicauda. It is slightly shorter (20-24 m on average) and mainly frequents the Indian Ocean and South Pacific. Its population is distinct from the North Atlantic one and considered relatively less depleted, though data remain incomplete.
Can amateurs contribute to blue whale research?
Yes. Platforms Happywhale and Obs-MAM accept photos of dorsal fins and spot patterns for photo-identification. Every clear shot can identify an individual and track its movements over years and thousands of kilometers. An equivalent focal length of at least 300 mm is recommended for usable images.