Slide Hammerhead Shark #2

Hammerhead Shark

SHARKS

The University of Florida is home to the International Shark Attack File (ISAF), started by scientists in 1958 and covering known shark attacks around the world going back to the 1500’s. The ISAF website and their annually updated statistics on unprovoked and provoked shark attacks across the globe are a testament to our fascination with sharks. With the amount of coastline and the number of people in the water in Florida, it’s not surprising that the state is prominent in ISAF statistics, but again the risk is very low. Since the time the Spanish settled Florida, reported shark attack comes out to two a year with a sharp increase starting in the 1970’s. Broken down further, there are seven reported attacks from Pensacola Beach since Spanish explorer Tristan de Luna landed here in 1559 – that’s right 7.

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The shark’s sensory system is one of the most amazing in the world. Tiny gelatinous cells along their sides detect pressure waves. Splashing, thrashing movements made by fish can be detected a mile away. It has been said that a shark can detect one drop of blood in thousands of gallons of water – and it is true. However, they must be down current of the victim. Their eyesight is also good. Sharks have “crystals” within their retina that act as mirrors – allowing them to see pretty well even in low light. They also have small cells in the head region that can detect small electric fields. When a shark takes the bait, it must close its eyes – they “roll back” into the head. At this point the shark is basically blind. However, if the prey moves out of the way, the weak electric fields produced in doing so can be detected and the shark knows where the target is.

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Nurse Shark

Blacktips and Spinners are grouped together because they resemble each other, and they are both common here. They are both stream-lined in shape and have blacktips on their fins. Actually, spinner sharks have more fins tipped-black than the blacktip. The anal fin of the spinner is tipped black, but this is not the case for the blacktip. Both species mate in the summer and have similar long gestation periods. The egg cases hatch inside the mother and she gives birth to live young around 2 feet long. The spinner only gives birth every other year and gets its name from the habit of leaping from the water and spinning very fast as it does so. Both reach about eight feet in length and unprovoked attacks are very rare.

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Blacktip Shark

The Nurse Shark is one of the bottom dwelling sharks that appear harmless – and they are – but if provoked, they will bite. Sharks lack a swim bladder and cannot float in the water column the way some fish do. Unlike other sharks that must swim constantly to keep water flowing over their gills, nurse sharks can rest on the bottom. They have less angular fins and are a brownish-bronze color, with small eyes. They possess a “whisker-like” appendage called a barbel. These are common on other bottom fish, like catfish, and possess chemo-sensory cells to detect prey buried in the sand. They are not as common here as they are in the Keys, but they typically reach lengths of up to nine feet.

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The look of a Hammerhead shark makes it clear how it got the name. There are several explanations for its aerofoil shaped head. 1) It is more aerodynamic, making it easier for this ram-jetter to swim. 2) It is a battery of sensory cells. By swinging the head back and forth, it’s like advanced radar searching for prey. 3) It is also believed they use their electric sense to detect buried prey – the shape making this easier to find and expose them. It could very well be that all of these could explain the shape. They have a tall dorsal fin which sometimes extends above the water when swimming near the surface – the classic “fin in the water” look. Unprovoked attacks have been known to occur with hammerheads.

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Hammerhead Shark

Since the film Jaws, the world has turned its attention from solely the white shark – to include the Bull Shark. As you can imagine, it is hard for a shark attack victim to report which species bit them. But studies since the 1970s, suggest that the bull shark is an aggressive species and may be responsible for a lot of attacks, particularly in the estuaries and upper estuaries. Bull sharks are what we call euryhaline – they have tolerance for a wide range of salinities.  This shark has been reported in low salinities of the upper estuaries and even into freshwater rivers. One report had them over 100 miles from the coast – they are certainly where the people are.

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Bull Shark

Thresher Sharks are bizarre looking sharks. Most sharks have what we call a heterocercal tail – meaning the upper lobe of the forked tail is longer than the lower. But the threshers take this to the extreme. Their tail can make up almost half of their body length, which can reach 20 feet. It is believed they use this extremely long tail to herd and stun baitfish – their favorite prey. They prefer colder waters and records in the Gulf are not common. Those that are out there live offshore and are rarely encountered near beaches. There are no unprovoked attacks reported from this shark.

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Thresher Shark

The Whale Shark is the largest fish on our planet and encounters are rare – but when they do happen, they are unforgettable. These are large sharks, with a mean length of 45 feet but some reporting in at 60 feet. They are easily recognized first by their size, but also their coloration. They are brownish color with beige or white spots in nice rows running across the dorsal side. They swim slowly while filtering plankton from the sea but will occasionally take in a fish. They are rarely seen because they tend to dive deeper during the day with the plankton layer – then coming closer to the surface at night following the same plankton. They are, unfortunately, sometimes struck by boats while at the surface.

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Whale Shark

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