Sharks often spark curiosity about their unique biology. One common inquiry pertains to their fate after death: do they float or sink? Unlike many other marine creatures, sharks possess distinct anatomical features that dictate their buoyancy, both in life and in death.
How Sharks Stay Afloat While Alive
Sharks employ several unique biological adaptations to maintain their position in the water column. A primary mechanism involves their large, oil-rich liver. This organ can constitute a significant portion of a shark’s body mass and stores a low-density oil called squalene. This oily liver helps reduce the shark’s overall density, providing a degree of static lift in the water.
The shark’s skeleton, composed of cartilage rather than bone, also contributes to its buoyancy. Cartilage is approximately half as dense as bone, making the shark’s frame considerably lighter and aiding in its ability to stay suspended. Beyond these anatomical features, sharks rely on dynamic lift, an active process generated by their movement. As they swim, their pectoral fins act like airplane wings, creating upward lift, while their heterocercal (uneven-lobed) tail provides thrust, helping to counteract their natural tendency to sink.
Why Sharks Typically Sink After Death
Immediately following death, sharks sink to the ocean floor. This occurs primarily because the active mechanisms that kept them afloat in life cease to function. The most significant factor is the loss of dynamic lift; without constant swimming, the lift generated by their fins and tail disappears.
Sharks also lack a gas-filled swim bladder, an organ common in most bony fish that allows them to precisely regulate their buoyancy. Unlike bony fish that can inflate or deflate this bladder to hover effortlessly, sharks depend on their oil-filled liver and continuous movement. Despite adaptations like the oily liver and cartilaginous skeleton, a shark’s overall density is still greater than seawater when dynamic lift is absent, meaning they are inherently negatively buoyant.
When Deceased Sharks May Float
While sharks typically sink upon death, their bodies can eventually resurface due to natural processes. This delayed floating is a result of bacterial decomposition. As bacteria break down the shark’s tissues, they produce gases within the body cavity. The accumulation of these gases causes the shark’s body to inflate, decreasing its overall density and making it buoyant enough to float to the surface. The time this takes varies depending on water temperature and the shark’s size.