Can Whales Smell? The Surprising World of Cetacean Olfaction

If you’ve ever witnessed a whale’s powerful exhalation at the surface, you’ve likely experienced the notorious “whale breath”, that pungent cloud that can clear a whale-watching boat deck in seconds. But while humans can certainly detect these oceanic odors, the question remains: Can whales themselves smell? The answer is more complex than you might expect, with significant differences between toothed whales (odontocetes) and baleen whales (mysticetes). So let’s dive into the science behind whale olfaction and discover how evolution has transformed their sense of smell as they adapted to life beneath the waves.

How mammalian smell works

Most land mammals have two key structures for detecting scents: the olfactory bulb, which processes general smells from the environment, and the vomeronasal organ, which specializes in detecting pheromones: chemical signals that convey information about reproduction, territory, and social status. These systems connect to specialized receptors in the nasal passages and transmit signals to the brain’s olfactory centers for processing.

For terrestrial mammals, smell is often a critical sense for survival: detecting predators, finding food, and communicating with others. But what happens when mammals return to the water? This is where the story gets interesting.

An evolutionary nose job

Whales descended from terrestrial mammals that once relied heavily on their sense of smell. Approximately 50 million years ago, their land-dwelling ancestors began the remarkable transition back to aquatic life. This evolutionary journey required dramatic anatomical changes, including one of the most extreme “nose jobs” in animal history.

As whales adapted to marine life, their nostrils gradually migrated from the tip of the snout to the top of the head, becoming what we now call blowholes. This repositioning allowed them to breathe efficiently at the surface while keeping most of their body submerged. A brilliant adaptation for aquatic life. However, this relocation had serious consequences for their olfactory system, disrupting the neural connections and airflow patterns necessary for effective smelling.

Baleen whales are hanging on to smell (barely)

Baleen whales (mysticetes), including humpbacks, blue whales, and right whales, retained some of their ancestral olfactory system during their evolutionary journey. Unlike their toothed cousins, they’ve preserved two separate blowholes and maintained some of their olfactory architecture.

Previous research revealed that baleen whales retained around half of their olfactory receptor genes, indicating they might still have some capacity for smell. However, their olfactory system is far from fully functional. Notably, they lack the dorsal domain of the olfactory bulb—a critical region in most mammals that helps detect and avoid noxious odors, such as rotting flesh.

What’s especially intriguing is how these whales may be using their limited sense of smell. Baleen whales may detect airborne scents primarily while surfacing to breathe. One of the key compounds they seem to respond to is dimethyl sulfide (DMS)—a chemical released when krill consume phytoplankton. Elevated levels of DMS in the air can signal biologically rich areas, helping whales zero in on prime feeding grounds filled with their favorite prey.

Toothed whales traded smell for sonar

For toothed whales (odontocetes), including dolphins, porpoises, belugas, and sperm whales, the evolutionary trade-off went even further. Their two nostril openings fused into a single blowhole, and their nasal passages were repurposed for something far more valuable in their underwater environment: echolocation.

The nasal passages in toothed whales now house phonic lips. They are specialized structures that produce the high-frequency clicks used for echolocation. Recent research has confirmed that toothed whales have lost virtually all functional olfactory genes. Their olfactory bulbs are either extremely reduced or entirely absent, and they lack the neural architecture needed for processing smells.

But recent research reveals toothed whales haven’t completely abandoned the chemical world. Scientists discovered what they call “quasi-olfaction“—a unique system that blends characteristics of both smell and taste. Instead of using the standard olfactory nerve pathway, dolphins may detect chemicals through their trigeminal nerve, which connects their mouth and nasal areas to the brain.

Scent Detection in Other Marine Mammals

Whales aren’t the only mammals that have adapted to aquatic environments, and each group has found unique solutions to the challenge of chemical sensing underwater:

Pinnipeds (seals, sea lions, and walruses) retain functional olfactory systems but can only smell in air, not underwater. They often raise their heads above water in a behavior called “periscoping” to sniff for danger or locate breeding colonies.

Sirenians (manatees and dugongs) still have small olfactory bulbs, meaning they likely can smell, but not as well as land mammals. They’re somewhere in the middle: not as smell-blind as dolphins and whales, but not super sniffers either.

Something smells fishy

When it comes to smelling underwater, fish are in a league of their own. Unlike mammals, they never had to transition from air to water breathing—they’ve been aquatic from the start. As a result, their olfactory systems are entirely separate from breathing and highly specialized for detecting waterborne chemicals. Water flows directly through their nasal passages, allowing them to pick up even the faintest chemical cues with remarkable precision.

In fact, fish are true scent connoisseurs. Some species can detect substances at concentrations as low as a few parts per million. Salmon, for instance, can recognize the unique chemical “fingerprint” of the stream where they were born, using it to navigate thousands of kilometers back home to spawn years later. Sharks take things even further: they can detect a single drop of blood in an Olympic-sized swimming pool and use differences in timing and concentration between their two nostrils to pinpoint its direction.

Scentless, but using other senses

Let’s face it: whales wouldn’t stand a chance in a sniffing contest against fish. While some baleen whales might catch faint whiffs of DMS in the air, most cetaceans have a limited or entirely lost sense of smell. Toothed whales may respond to chemical cues in water, but their olfactory systems are a far cry from those of their fishy neighbors.

Still, smell isn’t everything. In the world of whales, the ocean isn’t so much something to sniff—it’s something to hear, see, and feel. Their senses have evolved not for scent, but for sonar, vision, and touch, making them perfectly suited to life in the deep.

Sources and further reading

• Berta, Annalisa, Eric G. Ekdale, and Ted W. Cranford. “Review of the cetacean nose: form, function, and evolution.” The Anatomical Record 297.11 (2014): 2205-2215.
• Bouchard, Bertrand, et al. “Behavioural responses of humpback whales to food-related chemical stimuli.” PloS one 14.2 (2019): e0212515.
• Kishida, Takushi, et al. “Aquatic adaptation and the evolution of smell and taste in whales.” Zoological Letters 1 (2015): 1-10.
• Kremers, Dorothee, et al. “Sensory perception in cetaceans: part I—current knowledge about dolphin senses as a representative species.” Frontiers in Ecology and Evolution 4 (2016): 49.
• Ryan, Conor, et al. “Morphology of nares associated with stereo-olfaction in baleen whales.” Biology Letters 20.1 (2024): 20230479.
• Thewissen, J. G. M., et al. “Olfaction and brain size in the bowhead whale (Balaena mysticetus).” Marine Mammal Science 27.2 (2011): 282-294.