Category Archives: Sharks

Shark Bites in the USA

The USA has the most reported shark attacks in the world. What could be the reason for this? Are Americans so well nourished that they taste better? Could be, but all the references I have read say that a shark attack is most probably an “accident”. The shark had mistaken the human for his more usual meal such as a seal or another fish.

One reason the United States is at the top of the list is that the U.S. has a very large combined coastal shoreline. Another reason is the increase of recreational marine activities, and recreational marine activities expose people to all aquatic dangers including shark attacks.

No doubt, a high level of reporting of attacks is also a factor. Not all coastal countries publish a complete record of shark attacks. Publishing such reports could adversely affect the tourist trade. In addition to the USA some of the other countries that have reported shark bites are Africa, Central & S Am, Australia and Pacific Islands.

In the U.S 60% of all shark attacks are reported by the state of Florida. California reports about 15%, this is closely followed by Hawaii. Most coastal states have at one time or another reported a shark attack. Most of the attacks are not fatal. Most of the attacks are done by a contact bite, then the shark swims away. The victim can be left with a maiming wound or deformity. Fatal attacks are mainly due to the bull shark, tiger shark, or the great white shark and the Oceanic white tip shark. (Pictures and information about these sharks can be found at Dangerous animals–Sharks). In recent years the entire east coast has had a growing problem with aggressive sharks. The reason for the increase is being researched.

Overall shark attacks are extremely rare – “Lightning strikes humans more often than sharks bite humans”. The International Shark Attack File reports that world wide there are 50 – 70 unprovoked shark attacks a year. The number of shark attacks is increasing because the human population is increasing and recreational use of the shark habitat, oceans and coastlines, is increasing. Even though there are 50 to 70 attacks a year the number of fatalities are low.

Wikipedia has a list of the fatal, unprovoked shark attacks in the US. The records start in 1779 up to the recent. The more recent records state the age of the victims and other information that is interesting reading and gives some explanation of the event. A summary of the records show that there were 13 deaths from 2000 to 2010. Three of the years, 2002, 2006 and 2007, did not have any deaths. The years 2001 and 2004 had 3 deaths each. So far in 2010 there have been two reported deaths due to shark bites, but the year is not over.

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Dangerous animals–Sharks

We can all hear the ominous music, building slowly, frightfully, until the climax when Jaws attacks! Movies like Jaws have burnt this fearsome group of animals into our psyche, and I think the thought lurks somewhere in our minds whenever we visit the ocean that there are really big fish out there. There are somewhere around 440 species of shark worldwide. They are an ancient group of fish, whose overall lineage dates to before the Age of Dinosaurs. Of these hundreds of species, only 4 are known to have been involved in a significant number of fatal attacks on humans. Worldwide there is an average of 4.3 fatalities per year. 

The four most dangerous species have different habits, and therefore the patterns of attacks and their danger to people are different. They are the great white shark (Carcharodon carcharias), oceanic whitetip shark (Carcharhinus longimanus), bull shark (Carcharhinus leucas), and the tiger shark (Galeocerdo cuvier).

Great White Shark

Great White Shark

The great white, of Jaws fame, is a fearsome predator. Adult sharks are 12-17 feet in length. They are found along both coasts from Mexico into high latitude waters of Alaska, and along the east coast up to Hudson Bay. However, it is also known from deeper ocean waters, and new findings suggest that at least the west coast populations congregate in the open ocean between California and Hawaii for parts of the year. They are predators of marine mammals, turtles, large fish, and even whales. Humans are incidental targets.

During the hot summer of 1916, the Jersey Shore was the scene of a series of attacks that shuck the public, and was the inspiration for the book Jaws. Between July 1 and July 12, four people were killed. The great white is often blamed, but it could have also been a bull shark. Why there were so many attacks at that time is hard to say, and has not been repeated since.
Oceanic Whitetip Shark Oceanic Whitetip Shark

 

The oceanic whitetip shark is actually responsible for more fatal attacks on humans than all other species combined, and it does not even frequent the coasts. It is found worldwide, and prefers warm waters and deep ocean areas. It is the unfortunate events of the twentieth century that allowed this shark to become superlative in human fatalities—it is the shark reasonable for attacks on survivors of shipwrecks and downed aircraft. During the war in the Pacific, when ships and planes were regularly shot down, many hundreds of stranded sailors were attacked and killed. Horrific stories from survivors testify to this gruesome bloodshed and led to much research by the Navy in shark repellents. Hopefully, this scale of human carnage will never occur again. And while this species is the most deadly shark, its habits make it of little concern to the average beach-goer.

Tiger Shark Tiger shark

 

The tiger shark is found worldwide in mostly equatorial waters. It prefers tropical and sub-tropical warm water, and does not get into the high latitudes like the great white. It tends to stay in deep waters that line reefs, but it does occasionally move into shallow water and channels where it might encounter people. This shark is large, commonly attaining lengths of 10-14 feet, but because of its habits encounters with humans are relatively rare.

Bull shark Bull shark

 

In contrast, the bull shark is likely the most dangerous species to humans overall. It too is common in warm waters along coasts, but it also tolerates fresh water, and can migrate into rivers. They have been found far up the Amazon River in South America, and as far north in the Mississippi River as Illinois (yikes!) (Thomerson et al. 1977). These sharks are unpredictable and are often aggressive, and because of their habit of being in shallow waters are probably responsible for the majority of near-shore attacks.

However, having said all of that, the chances of being attacked are very remote. You can see the per year compared with other animals on the chart. Was that deep, ominous music I just heard?

Average number of deaths per year caused by various animals

Average number of deaths per year caused by various animals

Thomerson, J. E., T. B. Thorson, and R. L. Hempel. 1977. The bull shark, Carcharhinus leucas, from the upper Mississippi River, near Alton, Illinois. Copeia 1977(1):166-168.

Several of the images come from sources recommended in the Nature Wallpaper post.

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Shark bites in the Cretaceous Sea

One of the most exciting things in paleontology is being able to definitively establish the interaction of two species from the fossil record. It is thrilling to picture a moment in time, millions of years ago, when two animals were at the same place, at the same time, and be able from fossil evidence to glean something about their interaction and behavior.

One dramatic example of this is finding a fossil with clear evidence that it was bitten by a shark. During the Late Cretaceous, North America was cut in half by an interior sea that extended the Gulf of Mexico across the mid-continent to connect with the Arctic Ocean in the north, effectively creating two land masses where today there is one.

In this last period from the Age of Dinosaurs, fantastic and strange creatures swam the seas. Today, the sediments from that ocean are exposed in badlands across much of western Kansas, Nebraska, and South Dakota. These geologic formations, like the Niobrara Formation, preserve a rich record of the ocean life, and clearly show what a scary ocean it was.

Tylosaurus model from the Carnegie Collection

Tylosaurus model from the Carnegie Collection

Giant marine lizards thrived in the sea. These beasts, close relatives of modern snakes and lizards, were called mosasaurs. There were several kinds that likely had different modes of life, some making use of resources close to the surface, and other species specializing in deep-water feeding, with the largest of them reaching 50 feet in length. They were joined by another group of marine reptiles called plesiosaurs. Plesiosaurs occur in two basic body plans, with the unimaginative names of long-necked and short-necked for obvious reasons.

Long-necked plesiosaur Styxosaurus

Long-necked plesiosaur Styxosaurus

The long-necked plesiosaurs have been described as looking like a turtle with a snake threaded through its shell. They had a stocky, turtle-like body, enormously long necks capped by a remarkably small head, and stumpy tails. They had four large flippers that helped to propel them through the water as well.

Short-necked plesiosaurs had large heads attached to short, thick necks. The long-necked forms most likely specialized in eating smaller fish with their small heads, maybe using their long necks to “snake” their way amongst their prey before being noticed. The short-necked forms obviously ate large prey, as evidenced by their massive heads and powerful jaws. (You can find models of both long and short-necked forms, as well as mosasaurs as part of the collection of dinosaur toys).

Living alongside these giants of the sea were animals that we would easily recognize, at least for their general body plan—these were the sharks. There was a significant amount of shark diversity in the Interior Sea as well, from relatively small forms that likely ate near the sea floor, to mid-sized forms that ate smaller fish and scavenged on dead carcasses, to several very large species that rivaled the modern great white shark in size and ferocity.

On occasion, when finding remains of fish or the marine reptiles, we find evidence of those remains having been bitten by sharks. The most compelling evidence is when teeth are found embedded in the fossil remains, but also punctures and tooth scratches can be a telltale sign.

Several plesiosaurs have been found as partial skeletons, with bites in several areas of their body, suggesting that after they died and settled to the ocean floor their carcass was scavenged by mid-sized sharks.

Cretoxyrhina bites the back of a mosasaur in the Late Cretaceous

Cretoxyrhina bites the back of a mosasaur in the Late Cretaceous. Painting by Dan Varner.

And in one dramatic example, the great white of the Kansas seas bite the back of a mosasaurs, cutting a section of vertebrae completely out of the giant lizard. The section of back, with its included vertebrae, was later spit out by the shark after having been mostly digested. The gristly remains settled to the ocean floor to lie there for millions of years before being found and placed in a museum.

Today we are fascinated by tales of shark attack, with the movie Jaws being a prime example. You can learn about these dangerous animals in another post, but perhaps it gives you some comfort to know that the denizens of the ancient seas also were subject to shark bites!

Additional information about this specimen can be found at Oceans of Kansas.

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