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 track down their prey even from great distances. A sense of smell with superpowers.
Do you remember the scene from the Disney-Pixar animated film “Finding Nemo” where the great white shark Bruce inhales a single drop of Dory’s blood into his nostril? The apex predator had the noble goal of becoming a vegetarian. Shortly after, 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 predatory fish like sharks have nostrils when they don’t have lungs? And aren’t they also known for being able to smell a trail of blood from over a kilometer away? PETBOOK editor Louisa Stoeffler explains how this works and why it actually functions.
Why Shark Nostrils Work Differently
As with most fish, sharks breathe through their gills. These filter oxygen from the water, which then enters their bloodstream, supplying their organs with the vital substance and keeping their metabolism running.
The nasal opening—also called the 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 chimaera. Together, these animals belong to the group known as elasmobranchs.
Smelling Instead of Breathing – The Secret of the Shark Nose
Water flows passively into the naris as the shark swims, or in some species, it is actively drawn in by tiny, cilia-like hairs. This brings it directly to the rosette, where scent analysis begins—without the active sniffing that land animals are accustomed to. The depiction of the great white shark Bruce sucking in 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 confirmed 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.
To do this, sharks use currents that have carried the olfactory stimuli to their nose and then swim in the direction where they first detected the chemical scent—referred to in the study as scent filaments or odor plumes. 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
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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 these animals to navigate precisely in complex scent landscapes, such as those found in natural waters.
This ability seems evolutionarily significant: The farther apart the nostrils are, the finer the angles that can be resolved at higher swimming speeds. This could also explain the distinctive head shape of hammerhead sharks, whose widely spaced nostrils may provide 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 conservation organization “Sharkproject” explains this in the PETBOOK article: 11 Shark Myths Checked – Can They Really Smell a Drop of Blood from Miles Away?
Instead of reacting like Bruce from “Finding Nemo”: “Yummy! Just one bite,” the expert suggests a different scenario. Fish blood actually means for 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.”