Tag Archives: Predator

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.

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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

Crazy Life of the C-O Sole

When C-O Sole’s are first born they look like any other fish. But over time they go through a crazy metamorphosis that allows them to be one truly unique fish found in the waters of Catalina. If you were to break C-O Sole’s scientific name, Pleuronicthyes coenosus, down you would find that in Greek Pleuronicthys translates into “side” “fish” while coenosus translates to the Latin word “muddy.” This accurately describes the physical appearance of this fish.

Over time C-O Sole’s will go through a major transformation. As they grow older they begin to swim at an angle, either leaning more towards the right or more towards the left. But that’s not all! As they begin to swim more and more at an angle the eye that is found on the side facing down begins to force itself around their skull until it completely travels to the opposite side of their head. Soon after this eye movement occurs the C-O Sole will finish its transformation and spend the rest of its life as a flat fish.

CO Sole 3 CO Sole 1

But why go through all that effort? By going through this transformation C-O Sole’s have developed some amazingly unique features. First off their ability to camouflage is incredible! Being super flat allows them to fully cover themselves with sand and completely blend into their surroundings. And because both eyes are located on top of their head they have excellent vision, even when completely buried in sand. Their ability to hide within the sand is extremely beneficial when trying to escape the dangers found throughout the ocean.

C-O Sole’s are also excellent predators as well! They utilize their amazing camouflage skills to sneak up on their potential prey and use an ambush style technique.

Written by: Alex Feltes

Kellet’s Whelk: Meat-Loving Mollusc

When thinking of marine predators, snails aren’t usually the first animals that come to mind. The Kellet’s whelk is a type of carnivorous sea snail that lives in the sandy bottoms and kelp forests of the California coast, and inside its beautiful spiral shell lie a host of finely-tuned predatory tools and instincts. The Kellet’s whelk is the largest whelk species in California, growing up to seven inches in length. Its life span is unknown, but some scientists speculate they could live to be up to 50 years old. It spends its days scouring for meat on the ocean floor, either by scavenging on dead animals or by hunting sea snails, clams, and crustaceans. Like many other gastropods, whelks have sensitive chemoreceptors that allow them to “taste” the water for dissolved particles, helping them find food from a distance. A dead fish carcass will often attract several whelks from all over the ocean floor.

Kellet’s whelks hunt by using a long, muscular proboscis, which is a flexible appendage kind of like an elephant’s trunk. At the tip of the proboscis is a rough radula that acts as a file to grind away pieces of meat and shell. The Kellet’s whelk can extend its proboscis to over twice its body length, so it is able to reach food from a distance even if it lies in rock crevices that are two tight for its body to fit. If it is hunting another snail, the whelk will secrete digestive enzymes as it grinds a hole in the shell so it can suck out the body of the snail inside.

In recent years, a growing demand for Kellet’s whelk meat has turned it into a rising fishery, with most being taken as bycatch in lobster traps and sold to fish markets. Because the Kellet’s whelk is slow to grow and mature, they are vulnerable to being over harvested, and new research is being conducted to measure the ongoing effect that these new fishing practices will have on the whelk’s population levels.

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Written by: Megan Petkovic

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