Tag Archives: Senses

Sensitive Sharks! Everything You Want to Know!

According some experts estimations, sharks have been around planet Earth for somewhere between 425 and 450 million years making them just as old or even older than trees themselves! As such, sharks have had time to evolve numerous methods of sensing their environment, making them expert hunters. In order to understand shark senses, one must first understand where the perception of these different sensations occur in the shark brain.

The shark brain is a Y shaped organ located in the chondrocranium of the shark. The shark brain can be split up between the forebrain, midbrain and hindbrain, each of which will specialize in a different sense. The forebrains specializes in olfactory, midbrain in visual, and the hindbrain specializes in hearing, touch, and electroreception.

sharks

Depending on the species sharks can smell up to 1km or more away, hear about 100m away, see about 10m away depending on water clarity. Depending on the sharks environment/habitat there will be corresponding enlargements in the brain. If the shark lives in deeper water where not much light exist or live mostly in the open ocean where food availability tends to be low, they might have enlargements in their forebrains because they have to rely on olfaction to find their food. With over 400 different species of sharks, not all sharks are necessarily the “swimming noses” that we think they are. With such diversity, sharks will specialize in different senses based on the environment of which they live. Even with one sensory specialization, it is the combination of all the shark’s senses that make them such great predator.

sharks 1

As sharks draw in closer to their prey they use electroreception. Imagine the brain as a biological computer, sending electrical impulses down a highway of motor neurons in order to move the muscles of the body. Sharks are able to detect those electrical impulses from up to 1 meter away. Some sharks, such as the scalloped hammerhead, can sense as low as half a billionth of a volt of electricity. They use special gel filled pores called the Ampullae of Lorenzini in order to sense these weak electrical impulses.

sharks 3

Sharks will continue to dazzle and amaze us with their sensory capabilities. New research indicates that sharks can even use electroreception to navigate the earth by sensing the magnetic poles. Such extraordinary evolutionary advantages are what will continue to make sharks a dominant predator for a very long time.

COVER PHOTO CREDIT:

Brian Skerry, www.brianskerry.com from https://ocean.si.edu/ocean-life/sharks-rays/hammerhead-shark-sunset

References

Fig5

https://www.sharkbanz.com/pages/how-it-works

Fig4

http://blogs.uwa.edu.au/3dbrainprinting/files/2016/03/March_OB-x9twud.jpg

Fig.3

https://sharkopedia.discovery.com/wp-content/uploads/2015/07/sharkopedia-hierarchy-of-senses-550×350.jpg

Fig2

William E. Bemis 2016

Fig1

https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcScxaP3GxhkC1Xcxwn_Gyx1RT6CR5ujdp44RF9wYeC_dRcPshLV

Hammerhead video

https://www.smithsonianmag.com/videos/category/science/hammerhead-vs-stingray/

The Sixth Sense of Sharks

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

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.

Sources:

http://www.elasmo-research.org

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