Sharks Lateral Line
Sharks have long been known (and feared) for their impressive ability to smell even the tiniest traces of blood from miles away, despite being diluted by millions of gallons of seawater. For many decades, researchers believed that the animal’s ability to detect such tiny implications that prey was nearby existed entirely within its nasal passages. However, scientists have recently discovered that these ocean hunters make extensive use of the lateral line to detect and find their next meal.
The lateral line is present in most fish and is used to sense tiny vibrations in the water. It is situated just under the skin (subcutaneous) on the snout and along either side of the shark’s body. The lateral lines are canals that are filled with fluid. Tiny modified hair cells line its walls and are instrumental in sensing vibrations and movement.
These structures are so well tuned that they are able to detect frequencies as low as 25 Hertz. As vibrations make contact with these hair-like cells, they move and sway within the liquid. This causes messages to be transported via nerves to the brain, providing important information regarding the whereabouts and nature of the vibrations detected.
Interestingly, the lateral line can also locate odour plumes. These are 3-dimensional structures that assist the shark (and other bony fish) to detect prey as well as potential mates. Interestingly, when the lateral line of sharks is covered up or chemically impaired (as is the case when treated with certain antibiotics), they are often unable to detect these odour plumes or their sensory perception is somewhat limited, despite the fact that their nostrils are fully exposed and functional.
Usually, fish and sharks will use the combination of smell and turbulence detection at the same time. This process is called “eddy chemotaxis”. When a person, seal or other animal moves through the water, they leave behind them a wake (turbulence), which is infused with their body smell (odour). This is referred to as an “eddy”.
While it is optimal for the shark to be able to see its prey, it is really the combination of the lateral line and its sense of smell that makes for prime hunting abilities and opportunities for the animal. This is thought to be the reason that sharks often bump and rub up against objects and even divers, as it is believed to assist them to ‘taste’ whether it is suitable for consumption as they move the object against their lateral line.