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.
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.
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 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.
Nature has an incredible number of benefits—think of a time that you found solace in someplace wild. Or a time that you found yourself completely, utterly mesmerized by some odd creature. Perhaps your affinity for nature is more practical. We rely on nature to sustain our lives—nature provides us with the the oxygen we breathe, the water we drink, the land on which we build. Nature is also cause for inspiration. Scientists and engineers are now looking to nature to inspire new inventions. This is called biomimicry.
Biomimicry can be broken down like this: ‘bio’ comes from the Greek word for ‘life,’ and ‘mimicry’ comes from the Greek word for ‘imitate.’ Scientists, engineers, and researchers are quite literally looking to imitate life—it’s processes and other aspects. Here are some examples of biomimicry in action.
Shark Skin and Boats
Sharks have scales called dermal denticles. These scales, in some ways, resemble teeth on the shark’s skin. They feel rough to the touch, kind of like sandpaper. These scales make sharks extraordinarily hydrodynamic and they help protect against skin parasites. Researchers are looking into mimicking the structure and function of these scales to create a surface that can be applied to the hull of boats. The hope is that this surface will replace the toxic paints that are currently used.
Sea otters have incredibly dense fur to help them deal with the cold water in which they live. When otters dive into the water their fur traps little bubbles of air. Researchers at MIT are trying to mimic this mechanism in their creation of a wetsuit catered to surfers. Wetsuits these days rely the wearer’s body to warm up a thin layer of water trapped by the wetsuit.
There are plenty of fish in the sea. Seriously, there are. There are over 30,000 different species of fish around the world and they all have similarities and differences that have been documented through careful study over time. The study of fish is called ichthyology and people have been practicing ichthyology for millennia. The earliest form of fish study was learning the most efficient way to catch them. Learning how they bred and where their breeding grounds were was invaluable information.
Nowadays we know more about fish than ancient peoples could have imagined. We have learned that some of the biggest fish in the ocean begin their lives as microscopic plankton. Some fish journey for thousands of miles to breed at the same breeding grounds they were born at but had never returned to since. Some fish change from male to female and vice versa. The list could go way on.
When it comes to specifying fish there are three basic categories to place them in. the categories are Osteichthyes, Chondrichthyes, and Agnatha.
The class Osteichthyes is contains what most would consider the classic type of fish. These fish have skeletons that are made out of calcified bones, they have fused jaws, contain a swim bladder, and an operculum that covers their gills. The majority of the 30,000+ Species of fish belong to this class.
The second class of fish is Chondrichthyes. This class of fish is defined by their cartilaginous skeletons. The most recognizable members of this class are sharks but rays and skates are also members as well as other cartilaginous fish.
The last class is Agnatha. This bizarre class of fish is defined not by what it has but rather what it doesn’t. The Agnathans lack jaws and only have two living members, the lampreys and hagfish.
The study of fish is becoming more important every day with the growing human population. The increase in human population increases pressure on fish populations primarily the ones that are hunted for food. By fully understanding every aspect of a fish we can help insure that fish populations and Species will survive and potentially the human race as well.
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.
Swell sharks are pretty spectacular cartilaginous fish. True to their name swell sharks have the ability to puff up by sucking up air or water into their stomach allowing them to appear bigger to potential predator or threat. But how do these incredible sharks begin their life? In an egg of course! Female swell sharks are oviparous, meaning they produce eggs that develop and eventually hatch outside of the body. Females can produce as many as 4 eggs at a time and typically lay them among rock and algae. Within the egg case a large yolk provides 100% of the nutrition to the developing embryo. During their early stages of development they even posses external gills! Swell shark pups typically take about 9 to 12 months to fully develop – this time frame is at times dependent on the water temperature. In order to help themselves in the hatching process swell shark pups will develop two rows of enlarged dermal denticles on their back while they are still in the egg case. These enlarged denticles aid in the shark pushing itself out of the case! When they first emerge from the egg case pups are pretty tiny as they are only about 6 inches in length. These pups are fully independent once they hatch and must find food, such as benthic invertebrates, on their own.
According to ancient legends empty egg cases of swell sharks were considered to be mermaid purses.
Did you catch those incredible songs performed by our very own musically inclined friend, CIMI Shark?? Yep, we created that music to your ears to help you guys remember some of our favorite sea creatures that we sometimes see out on our snorkels!
We call these musical cartilage fish Chondricthyes, or cartilage fish. First, there’s the old DUH NUH NUH NUH NUH NUH NUH NUH NUH BATRAAAAY!!!! That’s the jive for our dear friend the bat ray, and you should sing it at the top of your lungs into your snorkel if ever you happen across one of these flapping beauties out in the water. We’ve got more songs where that came from, but of course we love most to hear the ones you come up with!
So what do our musical fish have in common? Sharks, Skates, and Rays are all cartilaginous fish, meaning they don’t have any bones! Instead, they get their structure from hard cartilage that mimics the same boney structures that we have in our bodies. Personally, I’d prefer a solid boney backbone, but these cartilage fish have something called a notochord, which helps provide structure as well as an ability to move with agility through the water. These cartilage fish also lack a ribcage, so if some of the bigger guys were to be taken out of the water, their own body weight would crush their internal organs! Ouch, let’s steer away from picking up a large shark anytime soon…
These musical cartilage fish are super neat because some of them, specifically sharks and rays, have things called dermal denticles. These dermal denticles, or skin teeth, are tiny sharp structures that overlap and provide protection as well as hydrodynamics, or an ability to swim fast in the water. If you’ve ever felt sandpaper, than you’re already familiar with what a shark’s skin feels like. Or if you’ve been to CIMI, than you certainly already know!
So what do all our musical fish have in common? Sharks, Skates, and Rays are made out of cartilage, meaning they have NO BONES!! We will leave you with a word of the wise: Don’t go challenging any of these cartilage Chondricthyes to any limbo contests, because they’d surely win!
Are you feeling nosy about these weird-looking skates? Don’t worry, we dug up some dirt on the Shovelnose Guitarfish just for you! +++= Image credit: Phil M. Roedel, Common Ocean Fishes of the California Coast
If you want a power chord, make it out of cartilage!
Cartilaginous fishes, or chondricthyans, such as sharks, skates, and rays, don’t have any bones — but they DO have a long spinal rod called a notochord, and bone-like structures resembling vertebrae but made of cartilage instead. Cartilage is softer and more flexible than bone, giving chondrichthyans the great swimming abilities and quick growth rates that make them top predators, or apex predators, in their habitats.
Sharks and rays wish they were cool enough for the SKATE PARK.
Guitarfishes are like a super-hybrid with all the best features of sharks and rays combined. Though they are cartilaginous fishes too, they are neither sharks nor rays but skates, which means they don’t have stingers, generally swim in a snake-like motion using their tail instead of an up and down flapping motion using their pectoral fins, and they are ovoviviparous, which means their young mature inside an egg INSIDE their mother until they are ready to hatch.
There are many types of skates (order Rajiformes, named for that “rajiform” snake-like swimming technique, for you nerds who were wondering), of which guitarfish are just one.
The family nose
Can you guess what the guitarfish family is called?
Here’s a hint: + + /2
If you said Rhinobatinae, the guitarfish family, you’re right! In Greek, rhinos means nose, and batis means ray. Rather than know them forever as ‘nose rays’ (and since they’re not rays at all!) scientists call this family of skates guitarfish. Guitarfish are an amazing hybrid have shark-like dorsal fins can get up to six and a half feet, or two meters, long, and some of them can have litters of 30 young at at time! There might be as many as 60 species in this family including guitarfish, wedgefishes, and fiddler rays. There are even a few species of freshwater guitarfish.
What kind do we see at CIMI?
There are many types of noses found in the guitarfish family, which also includes smooth nose, rough nose, broad nose, widenose, shortnose, and stripenose guitarfish! Here on Catalina Island we see the shovel-nose or pointed-nosed guitarfish, Rhonobatos productus. Shovelnose isn’t an insult — it’s a description of their pointed snout that helps them move through the water and bury themselves when they find a place to hide!
Shovelnose guitarfish can have up to 117 teeth. They are short and pebble-like, so in the unlikely event that a shovelnose bit you, you’d probably just feel a gummy nuzzle (it has only happened once in shovelnose history, and it was reportedly because a diver rudely interrupted a male guitarfish’s date). Since these skates don’t have stingers either, they are one of the safest animals to go hang out with in the water!
Some cool research in 2003 showed that the populations of shovelnose here in the Gulf of California have been isolated so long that they have started to develop genetic distinctions in their mitochondrial DNA (a really important portion of genetic material inherited from your mom). This might make them their own distinct species or sub-species, or tell us they’re on their way to becoming one!
These skates never stop growing throughout their lifetime, which is called indeterminate growth. They can live to be up to 16 years old, and the average mass of a shovelnose guitarfish is almost FIFTEEN POUNDS!
School of rock
Some guitarfish swim in large schools. This is not unheard of for chondrichtyans, but it is still interesting to note since many are solitary, territorial creatures.
How do I spot one?
Just look for two tiny holes next to each other on the sandy bottom, opening and closing like little blinking eyes. These are dorsal openings called spiracles, and guitarfish are using them to flush oxygenated water past their gills! They can bury their whole body in sand, but they have to keep their spiracles out to avoid breathing in sand. Gotcha, guitarfish!
What if I need help remembering the name of these pointy skates?
DON’T PANIC. Just tell someone this awful joke, and the shame will burn the shovelnose guitarfish into your memory forever:
What do shovels, noses, and guitars have in common?
They all get picked on.
But someone’s got to stand up for them. In fact, their most recent classification on the IUCN Redlist, the go-to list of threatened and endangered species published by the International Union for Conservation of Nature and Natural Resources, was “Near Threatened” in 2014, though no one has been able to gather accurate data on whether their populations are growing or shrinking. That’s why we picked the mysterious shovelnose to shine the spotlight on today… but we aren’t the only stop on the guitarfish’s tour. Check out their entry in the Animal Diversity Guide or their entry in Fishbase or this page about them on Oceana or this collection of awesome pictures to learn more about these amazing skates!
Horn Sharks (Heterodontus francisci) are a part of the family Heterodontadae. Horn Sharks can be identified by the spines in front of its two dorsal fins and spots throughout its body. It is commonly thought that they were named HornSsharks because of the spines but the true reason is because the ridges above their eyes appeared devil horned like. Their spines aid them against predators such as Angel Sharks, Elephant Seals and Bald Eagles. Horn Sharks rarely grow beyond 3ft in length and are usually spotted at night on the sandy bottom.
Heterodontus means different teeth because Horn Sharks, unlike most sharks, have flat molar like teeth that are used for crunching hard shelled animals like snails, sea stars, small crabs and some adults will even prey upon Blacksmith. The fact that they feed on bottom dwellers might explain why they are not the most graceful swimmers and prefer to spend most of their days hiding in or under dark places. Horn sharks are also well known because they lay eggs that are uniquely shaped like a screw so that the mom can wedge it between rocks and crevices to help it survive. The juvenile shark will stay inside the egg for up to 10 months before hatching and begin its life.
Because fish have gills instead of lungs, they must get their oxygen by taking it out of the water as it passes over their gills. If you have a fish tank at home, you know that bony fish, or members of the superclass Osteichthyes, are able to remain still or rest on the bottom of the tank. A bony plate covering their gills, called an operculum, is what allows Osteichthyes to achieve this water movement without swimming.
In a process called buccal pumping, water is drawn in through the mouth, or buccal cavity, while the operculum is closed. Then, the mouth closes and operculum opens, creating a one-way flow of water over the gills, allowing the fish to extract oxygen from the water without body motion.
Members of the class Chondricthyes, including sharks, skates and rays, have skeletons made of cartilage, and therefore do not have a bony operculum. Instead, they have 5-7 exposed gill slits. This does not mean, however, that all Chondricthyes must swim constantly to move water over their gills. But, some do! Large, pelagic sharks such as the great white shark, mako, whale shark, and blue shark are ram ventilators. This means that they move water over their gills by swimming and “ramming” the water into their mouths and over their gills. Some sharks, such as the sand tiger shark, can switch between modified buccal pumping and ram ventilation.
Benthic Chondricthyes, such as a horn shark, round ray, or shovelnose guitarfish, live on the sea floor, with mouths located on the bottom of their heads to get food from the sand below them. Many of these animals also camouflage and avoid predation or sneak up on prey by burying themselves in the sand. In order to breathe without buccal pumping or ram ventilation, they use specialized holes behind their eyes called spiracles. Spiracles act like a straw or snorkel sticking out of the sand, drawing water over their gills and out the gill slits. This allows these animals to remain motionless and below the sand while still being able to get oxygen. If you look closely at a shovelnose guitarfish hiding in the sand on Catalina Island, you can actually see the spiracles opening and closing behind its eyes!
We would like to thank you for visiting our blog. Catalina Island Marine Institute is a hands-on marine science program with an emphasis on ocean exploration. Our classes and activities are designed to inspire students toward future success in their academic and personal pursuits. This blog is intended to provide you with up-to-date news and information about our camp programs, as well as current science and ocean happenings. This blog has been created by our staff who have at least a Bachelors Degree usually in marine science or related subjects. We encourage you to also follow us on Facebook, Instagram, Google+, Twitter, and Vine to see even more of our interesting science and ocean information. Feel free to leave comments, questions, or share our blog with others. Please visit www.cimi.org for additional information. Happy Reading!