Blue whale communication is one of the more astonishing phenomena in the natural world. The animals produce calls in the 10-40 Hz range — at the absolute lower limit of what human ears can register, and well below the frequency of most ambient ocean noise — and those calls travel hundreds of kilometres through the deep ocean sound channel. A blue whale off Mexico can, under the right conditions, be heard by another blue whale off Hawaii. We don’t fully understand what they’re saying. We’re starting to understand more about how they’re saying it. The 2009 documentary Kingdom of the Blue Whale dedicated a substantial segment to the communication question, and Geography Scout’s marine specialist Tess Harrow has been waiting fifteen years for an excuse to write up the science properly. Here it is.
Blue whales are also the largest animal that has ever lived on Earth — larger than any dinosaur, larger than any other whale species, larger than any creature in the geological record by a substantial margin. The largest accurately measured individual was a 33.6-metre female taken by a whaling station in the South Atlantic in 1909, weighing an estimated 173 tonnes. The combination of unprecedented size and sophisticated long-range communication makes them, in our team’s view, one of the most consequential subjects in modern marine biology.
The Documentary’s Premise
The 2009 special followed a research expedition led by Dr Bruce Mate of Oregon State University and his colleagues, tracking blue whales across the eastern Pacific feeding and breeding grounds. The communication segment focused on the work of John Calambokidis, Kate Stafford, and other acoustic ecologists who have been recording and analysing blue whale vocalisations for decades. The episode walks through what is currently known about blue whale calls — their structure, their geographic variation, their suspected function — and what remains genuinely unknown.
The honest answer to “what do blue whales say to each other” is that we don’t know. We know they produce a small repertoire of distinct call types. We know the calls vary geographically (different “dialects” in different ocean populations). We know males produce most of the longer, structured “song” calls and that the song-call patterns shift with the breeding season. We know the calls travel improbable distances. We don’t know what the calls communicate beyond the broad inference that they support social coordination across distance.
The SOFAR Channel: Why the Ocean Carries Sound
The reason blue whale calls travel so far is a feature of ocean physics called the SOFAR channel (Sound Fixing And Ranging channel). At a depth of approximately 800-1,000 metres in most ocean basins, the combination of decreasing temperature and increasing pressure creates a layer where the speed of sound is at a minimum. Sound waves at certain frequencies, when emitted at this depth, are refracted back toward the layer rather than dissipating upward or downward. The effect is to create a natural waveguide that carries sound thousands of kilometres with minimal attenuation.
The SOFAR channel was discovered in the 1940s by US Navy researchers who developed it for submarine detection and rescue applications. Blue whales, of course, had been using it for tens of millions of years. The fundamental frequencies of blue whale calls — 10-40 Hz — are at the optimum frequency range for SOFAR propagation. The match is unlikely to be coincidence; it suggests strong evolutionary selection for calls tuned to the channel’s characteristics.
Hugo’s note: the math here is genuinely beautiful. The wavelength of a 20 Hz sound in seawater is approximately 75 metres. The blue whale’s body length is in the same order of magnitude. The whale’s body resonates at the wavelength it emits. The animal is, acoustically, an instrument tuned to its own communication channel.
The Call Repertoire
Blue whale vocalisations have been classified into a small number of distinct call types, with regional variations. The two most studied classes are “A calls” (short, low-frequency tonal calls, typically 15-20 Hz, lasting about 18 seconds) and “B calls” (slightly longer, more complex calls with a frequency-modulated structure, typically extending to about 25 Hz). Males in some populations produce these calls in regular sequences — A-B-A-B-A-B — that researchers describe as “song.” The song patterns vary between geographic populations: the eastern North Pacific song is structurally distinct from the western South Pacific song, which is distinct again from the Indian Ocean populations.
The geographic variation is one of the more interesting findings of the past two decades. Blue whales appear to have what humans would call dialects. Animals in different ocean basins produce structurally different calls, and the structure within each population is consistent across years. The implication is that calls are at least partly culturally transmitted — animals learn the dialect of the population they grew up in. This is rare in non-human species and aligns blue whales with the small handful of animals (other cetaceans, some songbirds) where vocal culture is genuinely heritable.
The Frequency Drop
One of the more puzzling findings in blue whale acoustic research is that the fundamental frequency of blue whale calls has been steadily decreasing across the past several decades. The eastern North Pacific population’s A and B calls have dropped from approximately 23 Hz in the 1960s to approximately 15 Hz in the 2010s — a substantial shift over a few generations. Mark McDonald, John Hildebrand, and others have documented this trend across multiple ocean basins.
The cause remains genuinely unclear. The leading hypotheses: post-whaling population recovery has increased acoustic crowding, and lower frequencies travel further with less inter-call interference; ocean noise from shipping and seismic survey has shifted what frequencies are clearly transmissible; sexual selection has pushed males toward lower (and presumably more attractive) calls; and a mass-related hypothesis that, as the population recovers and animals are larger and longer-lived on average, the optimal calling frequency shifts down with body size. None of these is decisively supported. The frequency drop is real, the cause is contested, and the implications for the species’ acoustic ecology are unknown.
The Anthropogenic Noise Problem
Modern ocean ambient noise is dominated, in the lower frequencies, by shipping traffic. The cumulative noise from the world’s commercial shipping fleet has approximately doubled the average ocean ambient noise in the 10-100 Hz band over the past several decades. Tess’s note: this is the band blue whales call in. The implication is that the effective communication range for blue whales has been progressively reduced as commercial shipping has expanded.
Quantifying the effect is hard. The best estimates suggest that the eastern Pacific blue whale population’s effective communication range has been reduced from many hundreds of kilometres to perhaps tens of kilometres in some heavily-trafficked regions. If this is accurate, it represents one of the largest and least-discussed anthropogenic impacts on a wild species in modern conservation. A blue whale off the California coast that, three centuries ago, could have heard another whale off Hawaii now operates in an acoustic environment closer to a noisy room than to the historical ocean.
The conservation response is incremental. Several international shipping organisations have voluntary speed-reduction programmes in major whale habitats (slower ships are quieter ships); a handful of port authorities have introduced incentive structures for quieter vessels; and there is ongoing IMO discussion of mandatory noise standards for new construction. Progress has been slow.
Strikes and Ship Routing
The communication research is part of a broader research programme that has substantial conservation implications. Blue whales are killed by ship strikes at a rate that is poorly quantified but is significant for the recovering eastern Pacific population. Acoustic monitoring data has informed decisions about commercial shipping lane re-routing in California, with the Santa Barbara Channel lane shifted in 2013 to reduce overlap with high-density blue whale feeding areas. Subsequent monitoring suggests the change has reduced strike rates measurably, though the data is sparse.
The combination of long-range acoustic monitoring (using passive sound recorders that can detect blue whale calls across hundreds of kilometres of ocean) and satellite tagging (Bruce Mate’s group has placed satellite tags on hundreds of blue whales over the past two decades) is now producing the data needed to manage the human-whale interaction at the scale required.
What the Documentary Got Right
The 2009 production handled the science with appropriate humility. It interviewed actual researchers (Mate, Calambokidis, others) rather than the generic “marine biologist” pool. It walked through the call types and the geographic variations clearly. It addressed the noise pollution issue without either overstating the catastrophe or downplaying the threat. The CGI visualisation of how sound travels through the SOFAR channel was, if anything, the best general-audience treatment of that physics we’ve seen.
The on-camera tagging sequences gave the audience an honest sense of what the field research actually involves — a small fast boat, a hand-held tag launcher, careful approach work, and a lot of sitting and waiting. Modern blue whale research is not glamorous work. The documentary respected that.
Where the Documentary Missed
The Krill question got too little attention. Blue whales are krill specialists; their feeding ecology is entirely dependent on the seasonal blooms of these small crustaceans across the Southern Ocean and the eastern Pacific upwelling zones. Climate-driven changes in krill distribution and abundance are arguably the single largest threat to blue whale populations going forward, larger than ship strikes, larger than residual whaling. The documentary acknowledges this in passing but doesn’t dedicate the screen time the issue deserves.
The Antarctic blue whale subspecies — historically the largest population, decimated by industrial whaling in the early 20th century — also gets less attention than the Pacific populations. The Antarctic blues remain the most endangered blue whale subgroup, with current population estimates well under 5,000 animals against a pre-whaling estimate of around 250,000. Their recovery has been slow and remains uncertain. A modern follow-up documentary could usefully focus on this population specifically.
Recent Work, Briefly
Since 2009, blue whale acoustic research has continued to develop. The Cornell University Bioacoustics Research Program and the NOAA Pacific Marine Environmental Laboratory have built increasingly sophisticated passive acoustic monitoring networks. The use of autonomous gliders carrying acoustic recorders has dramatically extended the spatial reach of the monitoring. Machine learning approaches to call classification have improved analysis throughput by orders of magnitude.
The current frontier in the science is correlation studies — linking specific call patterns to specific behavioural states (feeding, travelling, breeding, mother-calf interactions) using simultaneous acoustic and movement data. The hypothesis-rich answer to “what are blue whales saying” requires this kind of multimodal data, and it is now becoming available at scale. We expect significant findings in this space across the coming decade.
What to Watch and Read Alongside
For viewing, our team’s recommendations: David Attenborough’s Blue Planet II includes substantial blue whale footage and is the gold standard for current ocean documentary production. The BBC’s Whales: An Epic Journey covers the broader cetacean acoustic story. For reading, Carl Safina’s Becoming Wild includes excellent material on cetacean culture; Hal Whitehead and Luke Rendell’s The Cultural Lives of Whales and Dolphins is the academic gold standard for the cultural-transmission question.
For audio: the NOAA Sounds in the Ocean archive includes recorded blue whale calls that have been pitch-shifted up by several octaves to make them audible to human ears. Hearing one is unsettling and beautiful. We recommend it as the closest thing to direct experience of blue whale acoustic ecology that a non-cetacean can have.
Why It Matters
Blue whales are, by any reasonable accounting, one of the most remarkable species on Earth. They were brought to the brink of extinction by 20th-century industrial whaling and have only recently begun to recover. Their long-distance acoustic communication is a window into a sensory world humans cannot directly access. Their fate over the coming decades depends on our ability to manage shipping, noise, and the climate-driven shifts in their krill prey. Geography Scout will keep tracking the science. Tess says she’d still travel substantial distances to see one in the wild, and that the eastern Pacific feeding grounds (Monterey Bay; the California Channel Islands; the offshore Mexican waters around the Gulf of California) remain among the more reliable places to encounter them. Plan for it. They deserve the visit.
