Sharks

by Rick O'Connor | Jun 21, 2024

Today’s society is more educated about sharks and shark behavior than our forefathers.  In the 18th, 19th, and much of the 20th century we thought of sharks as mindless eating machines – consuming anything available.  Whalers would witness sharks consuming carcasses, as did many other fishermen.  Sailors noted sharks following the smaller boats across the ocean, always present when bad situations occurred.

During World War II the U.S. Navy was moving across the Pacific and a deeper understanding of sharks was needed to keep servicemen safe.  The sinking of the USS Indianapolis pushed the Navy into a larger research program to determine how to repel sharks and better understand what made them tick.  After the war funding for such research continued.  One of the leading researchers was Dr. Eugene Clark, who eventually founded the Mote Marine Laboratory in Sarasota with the intention of developing a better understanding of shark behavior.  Dr. Clark frequently appeared on the Undersea World of Jacques Cousteau educating the public about how sharks function and respond to their environment.  All with the idea of how to better reduce negative shark encounters.

Pregnant Bull Shark (Carcharhinus leucas) cruses sandy seafloor. Credit Florida Sea Grant Stock Photo

In the 1970s Peter Benchley wrote Jaws but included a marine biologist as one of the key characters who would provide science insight into how sharks work.  The film was a cultural phenomenon.  I remember standing in a line that wrapped the cinema twice to get in.  This was followed by more funding for shark research and a better understanding of how they work.  This was then followed by a popular summer series known as “Shark Week”, which remains popular to this day.  Many of the old tales of shark behavior were disproved or explained.  The idea of a mindless eating machine was replaced with a fish that actually thinks and responds to certain cues.  People began to realize that shark attacks are quite rare and could be explained if we understood what happened leading up to the attack.

We now understand that sharks are fish, in a class where the members have cartilaginous skeletons (they lack true bone).  They are one of the most perceptive creatures in the ocean, using their senses to detect potential prey and that there are signals that can “turn them on”.  On the side of their bodies there is a line of small gelatinous cells that can detect slight vibrations in the ocean – from up to a mile away.  The ocean is a noisy place, and it appears that sharks respond to different frequencies.  I like to use the analogy of yourself being in a large student cafeteria.  Everyone is talking and it is very noisy.  Then someone calls your name.  Somehow, amongst all the background clatter, you hear this and respond to it.  Studies suggest that sharks do the same.  With all of the noise moving though the ocean, sharks hear things that catch their attention and then move towards the source.

Blacktip sharks are one of the smaller sharks in our area reaching a length of 59 inches. They are known to leap from the water. Photo: Florida Sea Grant

As they get closer their sense of smell kicks in.  Everyone has heard that sharks can detect small amounts of blood in large amounts of seawater – remember “Bruce” from Finding Nemo?  It is true, but they do have to be down current to pick up the scent and they will now focus their search to find the source.  Some studies suggest other “odors”, such as the urine of seals, might produce the same reaction that blood does.  All may lead to shark to think a possible meal is nearby.

Eyesight is not great with any creature in the sea.  Light does not travel well in water – but sharks do have eyes and they do see well (one of the old tales science disproved – that sharks are basically “blind”).  However, because of the low light, they do have to be close to the target to get a visual.  Some studies suggest that sharks are detecting shadows or shapes they may confuse as a potential prey, bite it, and then release when they discover it was not what they thought it was.  This idea is supported by the fact that many who are bitten experience what is called “bite and release” – and they turn and swim away.  It is also known that sharks have structures in the back of their retinas that act as mirrors, collecting what light is available, reflecting it within the eye, and illuminating their world.  They believe they see pretty well at night – better than us for sure.  The image they see may appear to be a prey item and may be what is producing the vibrations and odors that they detected.

The Scalloped Hammerhead is one of five species of hammerheads in the Gulf. It is commonly found in the bays. Photo: Florida Sea Grant

And they have one more “sixth sense” – the ability to detect weak electric fields.  The shark’s mouth is not in position to attack prey as they move forward.  It is on the bottom of their head and, one of the old tales, was that sharks must swim over their prey to bite it.  Video taken during the filming for Jaws showed that the shape of the shark’s head changes at the last moment of an attack.  The entire head becomes distorted to get the mouth in the correct position for the bite.  The “eyes roll back” – as the old fishermen used to say – and the jaws move up and forward.  At this point the shark can no longer use its eyes to zero in on the target.  However, they have small cells around their snout called the Ampullae of Lorenzini that can detect the small electric fields produced by muscle movement – even the prey’s heartbeat – and know where they are.  But – they must be very close to the prey to detect this.

Understanding all of this gives scientists, and the public, a better idea of how sharks work.  What “turns them on” and how/when they will select prey.  One thing that has come from all of this is that we do not seem to be high on their target list.

The Great White shark.
Photo: UF IFAS

The International Shark Attack File is kept at the Florida Museum of Natural History in Gainesville.  It has cataloged shark attacks from around the world dating back to 1580.  The File only catalogs UNPROVOKED attacks.  With provoked attacks – those occurring while people are grabbing them, or fishing for them, or in some way provoked an attack – we understand why the shark bit the human.  It is the unprovoked attacks that are of more interest.  Those where the person was not doing anything intentionally to invite a shark bite, but it happened.

One thing we can tell from this data is that unprovoked attacks are not common.  Since 1580, they have logged 3,403 unprovoked shark attacks worldwide.  Considering how many people have swum in the ocean since 1580, this is a very small number.  Note, the File is only as good as the reports it gets.  In the past, many unprovoked attacks were not reported.  But in our modern age of communication, it is rare that such an attack does not make the headlines today.

The Bull Shark is considered one of the more dangerous sharks in the Gulf. This fish can enter freshwater but rarely swims far upstream. Photo: Florida Sea Grant

Of these attacks 1,640 (48%) have occurred in the United States, followed by 706 in Australia.  Many have explained this by the large levels of water activities people in both countries participate in.  In the US Florida leads the way with 928 unprovoked attacks (57%), most of these (351 – 34%) are from Volusia County.  This may be due to breakthrough emergency communications with Volusia County and thus more reports.  Many of the reports are minor, small bites from small sharks such as blacktips, but unprovoked none the less.  There are 26 unprovoked attacks logged from the Florida panhandle – 3% of the state total – and most of these (n=9) were from Bay County.

When looking at what people were doing when attacked, most were at the surface and participating in some surface water activity such as surfing, skiing, boogie boarding, etc.  This is followed by surface swimming or snorkeling.

This brings us to the attacks this summer in the panhandle.  There have been a lot of questions as to what may have caused them.  They are still assessing the situation before and during these attacks to try and determine why they happened.  As we have mentioned, we have learned a lot about sharks and shark behaviors over the last 50 years and several hypotheses are open for discussion.  We will see what the investigators learn.  Until then, the International Shark Attack File does offer a page on how you can reduce your risk.  There is “Advice to Swimmers”, “Advice to Divers”, “Color of Apparel”, “Menstruation and Sharks”, “Quick Tips”, “Advice to Spearfishers”, and “How to Avoid a Shark Attack”.  Read more on these tips at https://www.floridamuseum.ufl.edu/shark-attacks/reduce-risk/.