Sharks have been on this planet for a pretty long time, around 400 million years, and during that time have cemented themselves as some of the oceans top predators. One reason why these animals have been so successful is due to their incredible senses that allow them to smell, hear, and track down prey with incredible accuracy. Sharks however have a very distinct advantage over most of their fishy friends in the ocean, they can actually detect electrical pulses in the ocean to help them locate prey and navigate the oceans using an organ called the Ampullae of Lorenzini. This is called electroreception. Today, we are going to dive into shark infested waters and learn more about how this amazing sense works!
The Ampullae of Lorenzini are small clusters of jelly filled pockets that lead to jelly lined canals ending in small open pores located all over the heads of sharks. These pores can be easily seen on the heads of sharks as dark spots and run just underneath the skin centered around the nose and behind the eye (Fig 1). Interestingly, the ampullae of lorenzini is an extension of the lateral line that most fish have in the ocean to detect vibrations in the ocean. The jelly that is inside of these pores is called Keratan Sulfate and is the most conductible of all biological compounds! Shocking, I know. These canals are filled with multiple nerve fibers that run through the jelly lined canal connecting to the pore on the outside. Seawater is a great conductor of electricity which allows the ampullae to do its job. These organs are so sensitive that their threshold of sensitivity can be as low as 5 nV/cm, which means they can detect electrical currents as little as 5 billionths of a volt per square centimeter. Scientists believe that sharks, on average, have 1,500 ampullae on their heads and some can detect the difference of electricity when two AA batteries were connected 10,000 miles away.
Sharks are believed to have the strongest electroreception of any animal on the planet earth. Primarily, the ampullae of lorenzini is meant to pick up the weak electrical stimuli from their prey’s muscular contractions. It can even detect electrochemical fields emitted from paralyzed animals! Many bottom dwelling sharks use their ampullae to draw a picture of potential prey that rests under the sand without them even knowing the shark is intending to feast on them. Great Hammerheads use their large heads as metal detectors and wave them over the sand to located sting rays (Fig 2). This sense is especially useful when the shark is hunting in murky waters or at night. Sharks also use this ability to navigate through the earth’s oceans. The earth’s magnetic field surges through the oceans currents and is on the same magnitude as sharks are able to sense. So, sharks and rays are able to use the earth’s magnetic field for local orientation. This is paramount for Great White Shark migration as they swim 2,500 annually to get from reproducing waters to foraging waters. Another debatable use of the ampullae is that it can detect changes in temperature of the water as well.
There are many animals on this planet earth that have electro-receptive capabilities such as bees, platypus, and echidnas but none are on the same level as sharks and rays. It may seem scary that a shark can sense that you are swimming around them without them even seeing you, but remember that sharks are more threatened by us then we are from them.
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