June 17, 2025, 1:48 pm | Read time: 4 minutes
Sharks don’t breathe through their noses–but these seemingly useless openings are far from redundant. Behind the slits lies an astonishingly refined olfactory system that helps these predators detect their prey even from a great distance. A superpowered sense of smell.
Remember the scene from the Disney-Pixar animated film “Finding Nemo” where the great white shark Bruce inhaled a single drop of surgeonfish Dory’s blood into his nostril? The apex predator had the noble goal of becoming a vegetarian. Shortly afterward, however, his instincts took over, and the founder of the self-help group “Fish are friends, not food” tried to eat Marlin and Dory. But why do predators like sharks have nostrils when they don’t have lungs? And aren’t they known for being able to smell a trail of blood from over a kilometer away? PETBOOK editor Louisa Stoeffler explains how this is connected and why it actually works.
Why Shark Nostrils Work Differently
Like most fish, sharks breathe through their gills. They filter oxygen from the water, which then enters their bloodstream and supplies their organs with the vital substance, keeping their metabolism running.
The nasal opening–also called naris or olfactory pit–is a special organ of cartilaginous and bony fish. It consists of the naris and the nasal cavities behind it. There is no connection to the mouth and throat, so they are not used for breathing. Instead, there is a unique olfactory organ that primarily processes chemical sensory impressions.
Inside the naris is a multi-layered olfactory organ called the rosette. This detects scent particles in the water and varies in structure and complexity depending on the species of shark, ray, or catshark. Together, these animals belong to the group known as elasmobranchs.
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Water flows passively into the naris while the shark swims, or in some species, it is actively directed in by tiny, cilia-like hairs. This brings it directly to the rosette, where the scent analysis begins–without active sniffing, as land animals are accustomed to. The depiction of Bruce the great white shark essentially sucking up Dory’s blood is unfortunately not very true to nature.
A special feature of the shark’s sense of smell is its directional ability. If a scent is perceived more strongly on the left side, the shark can swim in that direction. However, scents behave differently in water than in air–they dissolve, move on different levels, and are distributed by currents.
This was also established in a 2010 study. A research team led by Jayne M. Gardiner (University of South Florida and Mote Marine Laboratory) and Jelle Atema (Boston University Marine Program and Woods Hole Oceanographic Institution) demonstrated in an experimental study that small sharks determine their direction of movement not by the strength of a scent stimulus, but by minimal time differences in the arrival of the scent at their two nostrils.
Sharks use currents that have guided olfactory stimuli to their noses and then swim in the direction where they first perceived the chemical scent–also called scent filament or odor plumes in the study. This allows sharks to detect a scent trail within seconds and follow it via the corresponding ocean current. This highly efficient olfactory system gives them an evolutionary advantage in the sea. 1
Sharks Smell “in Stereo” but Have No Appetite for Humans
The discovery that sharks use minimal time differences between their nostrils for directional determination represents a previously unknown model of olfactory navigation. “Stereo smelling” allows the animals to precisely orient themselves in complex scent landscapes, as found in natural waters.
This ability seems evolutionarily significant: The farther apart the nostrils are, the finer angles can be resolved at higher swimming speeds. This might also explain the distinctive head shape of hammerhead sharks, whose widely spaced nostrils could enable superior time resolution in scent detection.
And what happens if sharks smell human blood in the water? Dr. Iris Ziegler from the international shark and species protection organization “Sharkproject” explained to PETBOOK in this article: 11 Shark Myths Checked–Can They Really Smell a Drop of Blood Over Miles?
Instead of reacting like Bruce from “Finding Nemo”: “Yummy! Just one bite,” the expert suggests a different scenario. Fish blood actually means to the shark: “Yummy, I’m coming.” Whereas human blood triggers the following reaction in the animals: “I don’t know it, probably doesn’t taste good.”