Jonathan Peterson ‘23
Co-Executive Editor
The earliest known sharks date back to the Silurian period, more than 420 million years ago. However, modern sharks first appeared and diversified during the Jurassic period, between 200 and forty-five million years ago. Today, sharks are found in all seas but rarely in fresh water of any kind. The only common exceptions to this rule are the bull shark and the aptly-named river shark, both of which can swim in both seawater and freshwater. Sharks have a variety of adaptations that have made them so successful over their 420-million-year tenure. While this article will not necessarily be detailing the features of sharks that are most essential to their survival, I will do my best to discuss some of the more interesting aspects of sharks as a species.
Senses
Sharks are well known for their incredible sense of smell. Some species are even able to detect as little as one part per million of blood in seawater. This means that sharks can smell blood from hundreds of meters away, which would be comparable to a human being able to taste a single pinch of salt in about 2,000 pounds of potato chips.[1] Sharks are capable of identifying the direction a scent is coming from based on when their nostrils actually pick up the scent. This works similarly to how mammals determine the direction of sounds they hear. Finally, different species of sharks have different abilities when it comes to their sense of smell. Usually, these are based on environmental needs. For example, sharks which live in the dark depths of the ocean often have larger olfactory bulbs, meaning a greater sense of smell, than sharks which live in high visibility reefs.
Sharks and most fish also have what is known as a lateral line. This line, as the name would suggest, runs laterally down the body of the fish and allows them to detect speed and pressure changes nearby. This is generally useful for detecting struggling prey in the vicinity.
Perhaps the most intriguing sensory system of sharks is the ampullae of Lorenzini. These are electroreceptor organs found in the head of the shark. The organs are essentially mucus-filled pores with a bundle of nerves. They allow them to detect the electromagnetic fields that all living things produce. These allow sharks to find prey hidden in the sand by detecting these fields. One species of shark that makes particularly efficient use of this sensory system is the hammerhead shark. It is also believed that these organs may aid sharks in orientation and navigation, as the ocean currents moving in the magnetic field of the Earth also generate electric fields, which sharks may detect through their ampullae of Lorenzini.
Anatomy
I would like to highlight sharks’ remarkable skin. Sharks are covered in dermal denticles, rather than typical scales. These dermal denticles have been the source of much research and development in the competitive swimming world, although as someone who is not a scientist, it’s hard for me to determine what exactly the main benefit of these structures is. In short, a shark, instead of typical scales, has very small overlapping tooth-like structures (dermal denticle literally means “tiny skin teeth”). These structures are believed to help the sharks to swim more efficiently than other, scaled fish, while also affording similar amounts of protection, both from attacks by other fish and parasites. I’ve found conflicting reports on just howthese structures make sharks more efficient swimmers. Most seem to think that the shape of the structure significantly reduces the drag that sharks experience while swimming, meaning that they may go farther while spending less energy than they otherwise might. Another source theorized that the denticles might be creating low pressure zones in the water in front of the shark, literally pulling the shark forward into the low-pressure area. Another benefit of their skin is stealth. The ocean is, believe it or not, a rather noisy place. However, sharks have evolved to swim silently compared to their scaled brethren. Think of them like the owls of the sea. This adaptation may greatly increase their hunting prowess.
Lifespan
Sharks can live a long time. Generally, sharks live twenty to thirty years. Some, like the spiny dogfish, can live more than 100 years. And the Greenland shark is notorious for being the longest-lived vertebrate known to man. One Greenland shark specimen was 392 ± 120 years old, making it at least 272 years old and possibly as old as 512. Shockingly, the species doesn’t even reach sexual maturity until they are around 150 years in age.
Attacks
Sharks rarely attack humans. Only four species are involved in a significant number of fatal, unprovoked attacks on humans: the great white, oceanic whitetip, tiger, and bull sharks. In general, there is little identifiable pattern to unprovoked attacks. One of the things that one can do to avoid them is to first and foremost, stay out of the water. If that isn’t in the cards, avoid wearing jewelry or shiny metals. Excessive splashing may incite the shark into thinking you’re an injured fish, which can also cause an attack.
Some believe that shark attacks occur because of a case of mistaken identity—the shark believes that the human is a seal or some other prey item. While I have no evidence for my disagreement, I don’t buy this theory too much. Sharks are apex predators—I like to think they know what is and isn’t a seal just as well as I do.
Conclusion
Sharks are beautiful and interesting creatures. They do not deserve the fear associated with them, although a healthy dose of caution is never a bad thing. In fact, if anyone has a reason to be afraid, it is sharks. In 2021, it was estimated that the population of oceanic sharks and rays had dropped by 71 percent over the last half-century. These losses come from a mixture of climate change and, most importantly, illegal harvesting, often for shark fin soup. Poachers illegally fin millions of sharks each year, killing them in barbaric fashion. Sharks are captured, their fins are cut off while still alive, and the finless sharks are dumped back into the ocean, where they soon die of suffocation from being unable to pump water over their gills.
Further, shark fin soup is erroneously believed to be healthy. In fact, shark fins have a high concentration of the neurotoxin BMAA. Because of this, consumption of shark fins may actually pose a health risk.
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jtp4bw@virginia.edu
[1] Weird Science: Compare Your Sense of Smell to a Shark’s Sense of Smell, https://manoa.hawaii.edu/exploringourfluidearth/chemical/chemistry-and-seawater/elemental-abundance/weird-science-compare-your-sense-smell-shark-s-sense-smell#:~:text=Sharks%20can%20smell%20blood%20from,part%20per%20million%20(ppm).