Stephen Kade: How Sharks Sense their Food & Environment, August 9, 2018


NOAA Teacher at Sea

Stephen Kade

Aboard NOAA Ship Oregon II

July 23 – August 10, 2018

 

Mission: Long Line Shark/ Red Snapper survey Leg 1

Geographic Area: 30 19’ 54’’ N, 81 39’ 20’’ W, 10 nautical miles NE of Jacksonville, Florida

Date: August 9, 2018

Weather Data from Bridge: Wind speed 11 knots, Air Temp: 30c, Visibility 10 nautical miles, Wave height 3 ft.

Science and Technology Log

Sharks have senses similar to humans that help them interact with their environment. They use them in a specific order and rely on each one to get them closer for navigational reasons, and to find any food sources in the area around them. The largest part of the shark’s brain is devoted to their strong sense of smell, so we’ll start there.

Smell– Sharks first rely on their strong sense of smell to detect potential food sources and other movement around them from a great distance. Odor travels into the nostrils on either side of the underside of the snout. As the water passes through the olfactory tissue inside the nostrils, the shark can sense or taste what the odor is, and depending which nostril it goes into, which direction it’s coming from. It is said that sharks can smell one drop of blood in a billion parts of water from up to several hundred meters away.

Ampullae of Lorenzini and nostrils

Ampullae of Lorenzini and nostrils of a sharpnose shark

Sharks can also sense electrical currents in animals from long distances in several ways. Sharks have many electro sensitive holes along the snout and jaw called the Ampullae of Lorenzini. These holes detect weak electrical fields generated by the muscles in all living things. They work to help sharks feel the slightest movement in the water and sand and direct them to it from hundreds of meters away. This system can also help them detect the magnetic field of the earth and sharks use it to navigate as well.

Ampullae of Lorenzini and nostrils

Ampullae of Lorenzini and nostrils of a sharpnose shark

Hearing– Sharks also heavily use their sense of smell to initially locate objects in the water. There are small interior holes behind their eyes that can sense vibrations up to 200 yards away. Sound waves travel much further in water than in the air allowing them to hear a great distance away in all directions. They also use their lateral lines, which are a fluid filled canal that runs down both sides of the body. It contains tiny pores with microscopic hairs inside that can detect changes in water pressure and the movement and direction of objects around them.

Sight– Once sharks get close enough to see an object, their eyes take over. Their eyes are placed on either side of their head to provide an excellent range of vision. They are adapted to low light environments, and are roughly ten times more sensitive to light than human eyes. Most sharks see in color and can dilate their pupils to adapt to hunting at different times of day. Some sharks have upper and lower eyelids that do not move. Some sharks have a third eyelid called a nictitating membrane, which is an eyelid that comes up from the bottom of the eye to protect it when the shark is feeding or in other dangerous situations. Other sharks without the membrane can roll their eyes back into their head to protect them from injury.

dilated pupil of sharpnose shark

dilated pupil of sharpnose shark

Touch– After using the previous senses, sometimes a shark will swim up and bump into an object to obtain some tactile information. They will then decide whether it is food to eat and attack, or possibly another shark of the opposite gender, so they can mate.

Taste– Sharks are most famous for their impressive teeth. Most people are not aware that sharks do not have bones, only cartilage (like our nose and ears) that make up their skeletal system, including their jaw that holds the teeth. The jaw is only connected to the skull by muscles and ligaments and it can project forward when opening to create a stronger bite force. Surface feeding sharks have sharp teeth to seize and hold prey, while bottom feeding sharks teeth are flatter to crush shellfish and other crustaceans. The teeth are embedded in the gums, not the jaw, and there are many rows of teeth behind the front teeth. It a tooth is damaged or lost, a new one comes from behind to replace it soon after. Some sharks can produce up to 30,000 teeth in their lifetime.

Personal Log

While I had a general knowledge of shark biology before coming on this trip, I’ve learned a great deal about sharks during my Teacher at Sea experience aboard the Oregon II. Seeing, observing, and holding sharks every day has given me first hand knowledge that has aided my understanding of these great creatures. The pictures you see of the sharks in this post were taken by me during our research at sea. I could now see evidence of all their features up close and I could ask questions to the fishermen and scientists onboard to add to the things I read from books. As an artist, I can now draw and paint these beautiful creatures more accurately based on my reference photos and first hand observations for the deck. It was amazing to see that sharks are many different colors and not just different shades of grey and white you see in most print photographs. I highly encourage everyone that has an interest in animals or specific areas of nature to get out there and observe the animals and places firsthand. I guarantee the experience will inspire you, and everyone you tell of the many great things to be found in the outdoors.

Animals Seen Today: Sandbar shark, Great Hammerhead shark, Sharp nose shark

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