Undiscovered Ocean

The sei whale (pronounced 'say') is the third-largest animal on Earth, reaching up to 20 meters and 28 tonnes — and it is one of the most poorly studied of the great whales.

What makes sei whales distinct from all other large baleen whales: their feeding technique.

Most large baleen whales use lunge feeding — accelerating at prey aggregations and engulfing enormous volumes of water in a single explosive strike. Blue whales, humpbacks, and fin whales are all lunge feeders.

Sei whales primarily use skim feeding: swimming forward slowly at the surface with the mouth slightly open, filtering water continuously as they move. This is more like the technique of right whales than rorquals — unusual for an animal as closely related to blue and fin whales as the sei whale is.

Skim feeding targets: sei whales primarily eat copepods (tiny crustaceans, sometimes 1–2 mm in length) and sometimes euphausiids. Their baleen plates are the finest of any rorqual, allowing them to filter prey that other rorquals cannot retain.

Sei whales are highly migratory and unpredictable in their movement — appearing in areas in some years and absent in others, making them one of the hardest great whale species to study.

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Humpback whale milk is not like any milk you know.

It is extremely thick — the consistency of cottage cheese or toothpaste, not liquid. The high viscosity prevents the milk from dispersing too rapidly in seawater. And it is extraordinarily rich: approximately 35–45% fat — compared to roughly 4% fat in cow's milk and 3.8% in human milk.

A humpback calf drinks approximately 600 liters of this milk per day — and converts it into body mass with extraordinary efficiency. A newborn humpback calf weighs approximately 900 kg and is 4–5 meters long. During the nursing period, it gains approximately 30–45 kilograms per day.

Nursing takes place in warm breeding grounds where the mother is largely fasting — she has eaten almost nothing since leaving the summer feeding grounds. She is producing enormous quantities of extraordinarily rich milk by converting her own blubber reserves.

The calf must grow large enough, fast enough, to survive the return migration to cold polar feeding grounds — where it will learn to feed on krill and fish. The nursing period lasts approximately 10–12 months.

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In 2008, a team of researchers off northern Chile encountered something bizarre: a group of s***m whales floating motionless at the surface, completely unresponsive. The researchers carefully approached in a small boat — the whales didn't move. One whale was accidentally bumped by the boat. It startled awake.

The team had discovered, accidentally, how s***m whales sleep.

The behavior: s***m whales sleep in brief 10–15 minute sessions, floating vertically or slightly head-up at the surface, barely breathing, not moving. They do this in groups — likely for predator vigilance while sleeping. The sleeping sessions account for approximately 7% of the day — one of the lowest sleep fractions of any mammal.

The subsequent study published in Current Biology confirmed this observation and added depth data from biologging tags: the whales genuinely enter a sleep state, not just rest — their metabolic activity and responsiveness drop significantly.

S***m whales are thought to sleep differently from humans — potentially using slow-wave sleep (which can be done with only one brain hemisphere at a time) in very brief sessions to minimize vulnerability, rather than longer REM sleep cycles.

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***mWhale

One of the most remarkable discoveries in orca research: every pod has its own acoustic dialect — a set of calls unique to that pod that is passed down through generations by cultural transmission.

In the northeastern Pacific, the southern resident killer whales (three pods — J, K, and L — totaling approximately 73 individuals) each have distinct call repertoires. J pod, K pod, and L pod share some calls (these pods intermingle and together form a 'clan') but each also has calls unique to that pod.

Transient (Bigg's) orcas, which share the same waters, have an entirely different call structure — reflecting their different social organization and hunting strategy.

The system works because orca calls are learned, not innate. A calf learns its pod's calls from its mother and other pod members during the first years of life. The calls are refined and stabilized as the calf grows.

Scientists working with hydrophone recordings can identify which pod is present from a single call — no visual ID required.

Pods that share the same waters but have different dialects do not interbreed in the resident system — pods that cannot communicate in compatible dialects may be reproductively isolated.

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The beluga whale is immediately recognizable by its round, bulging forehead — the melon. But what makes the beluga uniquely extraordinary: the melon is deformable.

Belugas can change the shape of their melon voluntarily — flattening it, rounding it, depressing one side, or pushing it forward — by contracting the specialized musculature beneath the melon's lipid-filled tissue.

This is unique among cetaceans. No other whale or dolphin species has voluntary control over its melon shape to this degree.

The function: acoustic focusing.

The melon acts as an acoustic lens for the beluga's echolocation signals — focusing and directing the sound beam produced by the melon's fatty tissue acting on the ultrasonic pulses generated in the nasal passages behind it. By changing the melon shape, the beluga can steer its echolocation beam — shifting the focus of its sonar without moving its head.

Belugas are among the most sophisticated echolocators of any whale, capable of producing at least 11 different types of sound and echolocating prey through complex underwater environments including ice.

The melon shape changes are also potentially social signals — changes in melon shape are visible to other belugas and may communicate state or intent.

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A full humpback breach — the entire body leaving the water — is one of the most spectacular behaviors in the natural world. And it requires extraordinary power.

A 40-tonne humpback whale must accelerate from swimming speed to approximately 27 km/h to generate enough thrust to fully clear the water surface. This is achieved with a rapid series of powerful tail strokes, beginning from depth and surging upward on a near-vertical trajectory.

Why do they do it?

Several hypotheses have been proposed, and multiple functions may operate simultaneously:

COMMUNICATION — the impact creates a sound audible for kilometers underwater and above the surface. Breaching frequency increases in rough sea states, consistent with breach-as-long-range-signal.

PARASITE REMOVAL — the impact force may dislodge barnacles and whale lice.

SOCIAL DISPLAY — breaching is more frequent in competitive male groups and social surface-active groups, consistent with a display function.

PLAY — young calves breach repeatedly in calm conditions with no obvious functional trigger, suggesting practice or play.

The most likely answer: all of the above, with the dominant function varying by context.

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Every year, the eastern Pacific gray whale population makes a round-trip migration of approximately 15,000–20,000 kilometers — the longest migration of any known mammal.

The route: from summer feeding grounds in the Bering and Chukchi Seas off Alaska, south along the west coast of North America, through the coastal kelp beds and into the warm lagoons of Baja California, Mexico.

In Baja, females give birth in warm, shallow lagoons — places like Laguna Ojo de Liebre and San Ignacio Lagoon — where the calm water protects the newborn calves. The calves grow rapidly on high-fat mother's milk for approximately 8 months before the return migration.

Then the round trip begins again — north, back to the Arctic feeding grounds.

Gray whales swim slowly — typically 6–9 km/h — but migrate continuously, navigating by the Earth's magnetic field, ocean temperature gradients, water turbidity, and possibly the sound of the coastline. They stay in shallow coastal water for most of the migration — making them the most accessible of all the great whales from shore.

The record individual: a western Pacific gray whale nicknamed 'Varvara' was tracked migrating 22,511 km in one direction — the longest recorded movement of any animal on Earth.

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When researchers spent four winters recording bowhead whales in the Bering Sea, they were shocked by what they found: bowhead whales had more than 60 distinct song types — and virtually none repeated between winters.

The study, published in Biology Letters, analyzed 1,000+ different songs recorded by hydrophone over four years. Each year, the bowheads were essentially singing a completely new repertoire.

Humpback whale songs are impressive — males sing one shared song that evolves gradually. But bowheads appear to operate on a different level: they are improvising constantly, with tremendous individual variation, and the song repertoire completely turns over across years.

Why? The researchers don't know. The bowhead whale song system doesn't fit neatly into either the female-choice model (which predicts a shared, stable 'best' song) or the male-rivalry model (which predicts consistent advertisement signals).

One possibility: bowheads live for 200+ years and are intelligent enough to maintain a far more complex, open-ended vocal system than any other whale — one where novelty itself is the signal, or where individual identity is communicated through vocal style that changes continuously.

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The fin whale is the second-largest animal that has ever existed — reaching lengths of up to 27 meters and weights of up to 80 tonnes. Only the blue whale is larger.

But the fin whale outperforms the blue whale in one striking way: speed.

Fin whales have been recorded at sustained swim speeds of 35–40 km/h and short burst speeds up to 47 km/h — earning the nickname 'greyhound of the sea.'

The anatomy behind this: the fin whale's body is significantly more elongated and streamlined than the blue whale's. The dorsal fin is taller and more falcate (curved), reducing drag at speed. The muscle mass is distributed for high-output forward propulsion.

One of the most distinctive features of the fin whale: the jaw is asymmetrically colored. The right lower jaw is white; the left lower jaw is dark. This asymmetry extends to the baleen plates (lighter on the right, darker on the left) and is unique among large whales. It may be related to the whale's feeding strategy of rolling to its right side as it lunges.

Fin whales were among the most heavily hunted whales during the commercial whaling era — over 700,000 were killed in the Southern Ocean alone.

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The humpback whale song is one of the most studied animal communication systems on Earth. And yet, after six decades of research, a fundamental question remains open: does female choice drive the evolution of the song?

What we know:
• Only males sing
• Males sing during the breeding season
• The song is complex and structured (themes, phrases, units — a hierarchical sequence)
• The song changes every year, with innovations spreading across ocean basins
• All males in a population sing the same song at any given time

What we don't know:
• No confirmed direct observation of a female approaching or responding to a singing male in a way that clearly indicates mate choice
• Males singing on a breeding ground are usually ignored by females swimming past — females that are receptive are typically quickly surrounded by multiple males in rowdy groups
• The function of song may be male-male rivalry rather than female attraction — advertising size, fitness, or location to other males

The honest answer from the science: the song almost certainly has a sexual function, but the precise mechanism — female choice, male-male signaling, or both — remains one of the great open questions in marine mammal biology.

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