How Do Sharks Breathe?

Sharks, like other fish, rely on their gills to breathe. Gills function similarly to human lungs, allowing sharks to extract oxygen from water. Each gill contains numerous fine filaments lined with lamellae, which house tiny blood vessels called capillaries. These capillaries absorb oxygen from water while simultaneously releasing carbon dioxide. Surprisingly, sharks can extract up to 80% of the oxygen available in water, whereas humans only absorb about 25% of the oxygen in the air.

Unlike most fish, sharks lack an operculum (gill cover). Instead, they rely on a process known as ram ventilation. This method involves swimming forward to push water through their open mouths and over their gills, ensuring a constant oxygen supply. Some sharks, like the great white and mako, have an additional gill slit known as a spiracle behind their eyes, which helps direct water through the gills, enhancing their breathing efficiency.

A shark's circulatory system is quite different from that of humans. Their two-chambered heart pumps oxygen-rich blood from the gills to the rest of the body. However, the heart alone isn't strong enough to maintain circulation, so the flow of water assists in moving blood through their system. This unique adaptation allows sharks to conserve energy while ensuring their organs receive the necessary oxygen.

When sharks swim faster, their breathing and circulation become even more efficient. This phenomenon, known as the ramjet principle, allows them to chase prey without exhausting themselves. Their blood flows in the opposite direction of incoming water, maximizing oxygen absorption and improving overall efficiency.

While some sharks rely on constant motion to breathe, others use a technique called buccal pumping. This involves using their cheek muscles to actively pull water into their mouths and over their gills. Some modern shark species, such as nurse sharks and angel sharks, still use this method, allowing them to remain stationary while breathing.

Sharks that spend most of their time near the ocean floor have adapted to breathe while staying still. Their flattened bodies and specialized spiracles help them draw in water even when buried in the sand. This adaptation makes bottom-feeders like carpet sharks well-suited to their sedentary lifestyles.

Some sharks can switch between buccal pumping and ram ventilation, depending on their activity level. For example, sand tiger sharks can alternate between these methods as they hunt along the ocean floor or swim through open waters. This flexibility allows them to optimize their energy usage and adapt to various environments.

Certain shark species, known as obligate ram ventilators, have lost the ability to breathe through buccal pumping altogether. These sharks, such as great whites and whale sharks, must swim continuously to survive. Without constant movement, they risk suffocation as water flow through their gills ceases.

Despite needing constant movement, some sharks can rest by using environmental factors to their advantage. For instance, reef sharks have been observed resting in oxygen-rich waters, like those found in underwater caves. These areas provide enough dissolved oxygen to allow the sharks to remain still without suffocating.

While sharks have survived for millions of years, modern challenges put them at risk. Illegal finning operations leave many sharks unable to swim, leading to their death by suffocation. Additionally, fishing nets and unregulated captivity environments often result in fatalities due to a lack of understanding of their breathing needs. Conservation efforts are crucial to ensuring the survival of these incredible creatures.