Sharks have been around for hundreds of millions of years, but sadly, many sharks are now under threat. Understanding how sharks die – both from natural causes and human activities – can help us better protect these critical ocean predators. In this blog post, we’ll explore how sharks meet their demise.
How Do Sharks Die?
Sharks can die from various causes, both in the wild and due to human activities like overfishing. Here are some of the main reasons sharks die:
Overfishing
Overfishing is a significant threat to many shark species. Sharks are highly valued for their fins, meat, and other body parts and are overfished in many parts of the world. When too many sharks are caught, it can deplete populations and lead to species decline and death.
Overfishing occurs in both directed shark fisheries and as bycatch in other fisheries. The demand for shark fins for shark fin soup drives much of the directed shark fishing. Bycatch occurs when sharks are accidentally caught by fishermen targeting other species. Since sharks have slow reproductive cycles, overfishing can quickly decimate populations.
Old Age
In the wild, most sharks die from old age once they reach the end of their natural lifespan. Sharks have a wide range of longevity – some species live for only 10-15 years, while other shark species can live for decades or even a century in rare cases.
As sharks age, their organs and tissues gradually deteriorate, they may starve due to worn teeth, and their immune systems weaken. Older sharks often suffer from infections, tumours, cardiovascular disease, and muscle degeneration. For old sharks, a lack of energy to hunt effectively eventually leads to their death.
Injuries or Diseases
Like all animals, sharks can suffer injuries from encountering boats, fishing gear, or marine debris. Deep wounds and significant blood loss can kill sharks. Sharks also face dangers like parasites, bacterial or viral infections, and various debilitating diseases as they age.
Sick, stressed sharks with compromised immune systems have difficulty fighting these health issues, which can eventually kill them. Injuries or diseases are most dangerous for lone sharks since being in a group helps defend against threats.
Predators
While sharks are apex predators, younger and smaller sharks can still fall prey to other large shark species, such as tiger and great white sharks. Killer whales also hunt sharks, including great whites.
Sharks evolved as prey, just like other animals. But since they mature slowly, losing younger sharks to predation hinders repopulation. This natural predation becomes problematic when shark populations are already depleted.
What Happens to a Shark’s Body When It Dies?
When a shark dies, a fascinating process unfolds as the shark’s body sinks through the water column to the seafloor. Here’s an overview of what happens:
- After death, the shark’s buoyancy changes. The liver holds oil that helps sharks maintain neutral buoyancy. This oil breaks down after death, causing the shark to sink.
- As the lifeless shark sinks, scavengers start consuming the body. Small hagfish and crabs may enter the mouth, gills, or wounds and start feasting. Larger scavengers like sleeper sharks may rip off chunks of the carcass.
- Through this feasting, gases build up inside the shark’s body. This bloating causes the shark’s belly to swell. The swell eventually rips open, releasing oil and internal organs as the shark continues to sink.
- By the time the shark carcass reaches the seafloor, much of the soft tissue has been consumed. This leaves the skeleton, jaws, and sometimes fins for bottom-dwelling scavengers to pick over.
- Over time, the remaining shark cartilage and bones decay and become covered in sediment. This leaves behind fossilized shark teeth and vertebrae known as Ichthyoliths.
So, in essence, a dead shark body provides one last critical meal for various marine species as it descends through the water column.
Do Sharks Die If They Stop Moving?
A common myth is that sharks die if they stop moving. So, do sharks have to keep swimming to breathe?
The answer is no. Sharks do not die if they stop moving. Like all fish, sharks have gills that extract oxygen from water as it passes over them. As long as oxygenated water flows over their gills, sharks can breathe.
Sharks need to keep water moving over their gills to get oxygen. But they can do this without constantly swimming forward. Species like nurse sharks have spiracles that pump water over their gills, allowing them to rest on the seafloor.
The myth may have started because sharks do need to swim constantly to pass water over their gills. If water isn’t moving over their gills, they will suffocate. But they don’t have to swim to make this happen actively. Water can be moved over their gills by ocean currents.
So, in reality, many species of resting sharks open their mouths to allow new oxygenated water to be flushed over their gills. They can even rest and sleep this way. They only die if the water stops moving, preventing their gills from extracting oxygen.
Do Sharks Drown When They Die?
No, sharks do not drown when they die. As explained above, sharks extract oxygen from water using gills rather than lungs.
The equivalent of drowning for sharks is suffocation. A shark suffocates when water stops moving over its gills, preventing oxygen uptake. This can happen if a fishing net blocks water flow over their gills.
But usually, sharks meet their demise in other ways, like old age, disease, or predation. A shark dying from natural causes still has water flowing over its gills even as it takes its last breaths.
So, technically, sharks do not experience the sensations of drowning that humans feel. They suffocate as their gills are starved of oxygenated water. But the end result is the same – no oxygen means death.
Average Shark Life Expectancy
Shark life spans vary drastically between species. Here are some examples:
- Spiny dogfish sharks: 35-40 years
- Bull sharks: 12-15 years
- Great white sharks: 70-100 years
- Whale sharks: 80-100 years
The Greenland shark has the longest known life span of all sharks, living approximately 400 years!
Shark life expectancy depends on genetics, diet, predation risk, and hazards faced. Slow-growing large shark species that produce few offspring tend to live longer. Fast-growing smaller sharks with high reproductive rates often have shorter lives.
In general, most sharks seen by humans are juveniles or young adults. Older sharks make up a smaller proportion of the population. Measuring shark ages is also tricky – it requires examining growth rings in vertebrae under a microscope.
Given the threats sharks face worldwide, most species today do not live out their full natural life expectancy due to fishing mortality, ship strikes, pollution, and other hazards. Allowing sharks to reach old age could require targeted conservation efforts.